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Toxicity Effects

CAS Registry Number: 150-13-0

Selected toxicity information from HSDB, one of the National Library of Medicine's databases. 2.

Names 1

  • 4-Aminobenzoic acid
  • Benzoic Acid, 4-Amino
  • Paba
  • p-Aminobenzoic acid

Human Toxicity Excerpts

  • CASE REPORTS: A 6-year-old girl with xeroderma pigmentosum was contact and photocontact sensitized to PABA which had been used as a sunscreening agent. The activating wavelengths for photocontact dermatitis were in long-wave ultraviolet light. Although PABA is the most effective and harmless sunscreening agent for normal skin, it could induce photocontact sensitivity especially in diseased or damaged skin.[Horio T et al; Dermatologica 156 (2): 124-8 (1978)] **PEER REVIEWED** PubMed Abstract
  • CASE REPORTS: A case report described that the potassium salt of PABA (administered orally 4 g three times a day for about 2 months) to a 64-year-old woman led to hepatotoxicity in a patient with scleroderma, as evidenced by elevated serum alanine aminotransferase and aspartate aminotransferase. /Potassium salt of PABA/[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • CASE REPORTS: A case report regarding a 51-year-old man admitted to the hospital with a seven-day history of progressive myalgias, generalized weakness and fever. The man had been treated with PABA 3 g four times a day for four weeks for Peyronie's disease. After discontinuation of PABA his fever abruptly returned to normal, the myalgias and weakness resolved and a decrease in the transaminases occurred within 24 hours. Normalization of his transaminases occurred in 10 days. Hepatic injury has not been widely considered to be potential adverse effect of PABA's administration. However, this case report shows that PABA may cause hepatic injury.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • CASE REPORTS: Human tests performed on patients contacting a dermatological clinic with a suspected skin disease shows that PABA has a potential to cause photo allergy reactions. Considering the fact that the results are based on patients with suspected dermatological problems rather than the general population, the prevalence is likely to be lower in the general population than in the studied groups. The highest photo allergy reaction to PABA was found in a Norwegian study from 1980 - 82 on 23 patients where 21.7% reacted. In most ... /studies/ the reaction to PABA was in the range 0 - 3%.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • CASE REPORTS: In a patient with no prior history of cutaneous reactions to other sunscreens or topical anaesthetics, PABA did not show contact allergic reactions when patch tested were protected from sunlight. When PABA was tested in alcohol and when the site was exposed to UVA irradiation the patient showed photo-contact allergic reactions.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • EPIDEMIOLOGY STUDIES: The Scandinavian photopatch test procedure has been applied to 745 patients with suspected photodermatoses during the years 1980-1981. /The authors/ experience has been encouraging with the recording of several relevant reactions. A total of 132 positive photocontact reactions and 120 ordinary contact reactions were seen. Photocontact reactions to...PABA (19 cases) were surprisingly frequent... Ordinary contact reactions were observed to balsam of Peru (30), PABA (23), lichen mix (21), wood mix (14) and to perfume mix (10).[Wennersten G et al; Contact Dermatitis 10 (5): 305-9 (1984)] **PEER REVIEWED** PubMed Abstract
  • EPIDEMIOLOGY STUDIES: The level of positive photo allergy reactions to PABA is in the same order of magnitude in the various countries, except for a Norwegian study that showed a level 10 times higher than results from the other countries... The number of photo allergy reactions to PABA tends to decline in European studies during the period 1990-2000 compared to the period 1980-1989. Overall, the decline is insignificant since the retrospective studies spanning both decades have chosen to publish one value for the entire time span. Despite the insignificant decline, many papers explain the tendency to decline by the reduced use of PABA during the last decade.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • HUMAN EXPOSURE STUDIES: In a dermatological clinic in Norway 23 patients with reactions to sunscreen preparations were seen during the years 1980-1982. The symptoms were eczema, redness, stinging or burning of the face following sun exposure. Patch tests and photopatch tests were carried out on the patients. Allergy to PABA was demonstrated in 11 patients (48%), of which 6 had plain contact allergy (26%) (PABA on non irradiated test sites) and 5 (21.7%) reacted to PABA only after irradiation.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • OTHER TOXICITY INFORMATION: The manufacturers of sunscreen preparations with propellants warn that concentrating and subsequently inhaling the fumes from these preparations may be harmful or fatal. /Propellants/[American Society of Health-System Pharmacists 2013; Drug Information 2013. Bethesda, MD. 2013] **PEER REVIEWED**
  • OTHER TOXICITY INFORMATION: The phototoxic and photoallergic effects of the once popular UV sunscreen p-aminobenzoic acid are related, in part, to its ability to sensitize the formation of singlet oxygen as well as other reactive oxygen species. In this work /the authors/ demonstrate that the sunscreen-photoinduced inactivation of a model protein, horseradish peroxidase, is reduced by approximately a factor of three when the sunscreen is encaspsulated in zeolite sodium Y. These results provide evidence that using the technology of zeolite encapsulation to prepare a supramolecular sunscreen that minimizes the skin contact of active ingredients may reduce the adverse effects of "naked" sunscreens on biological systems. These radiation-induced effects, unfortunately, frequently accompany the desirable UV-screening role of these products. These results provide an important benchmark for the use of zeolite encapsulation as a means of improving the safety of UV sunscreens for topical application. /Supramolecular sunscreen/[Chretien MN et al; Photochem Photobiol. 82 (6): 1606-11 (2006)] **PEER REVIEWED** PubMed Abstract
  • OTHER TOXICITY INFORMATION: Through the years 1995-2004 complaints related to the use of the sunscreen product amounted 22 certain or dubious allergies on average per year (range 8-36), corresponding to 0.0049% (range 0.0034-0.0071%) complaints per unit of sold sunscreen product. The frequencies of certain or dubious allergies were on average 0.0018% and 0.0031%, respectively.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • OTHER TOXICITY INFORMATION: Topical use of sunscreens reduces the risk for sunburn in humans. Sunscreens probably prevent squamous-cell carcinoma of the skin when used mainly during unintentional sun exposure. No conclusion can be drawn about the cancer-preventive activity of topical use of sunscreens against basal-cell carcinoma and cutaneous melanoma. Use of sunscreens can extend the duration of intentional sun exposure, such as sunbathing. Such an extension may increase the risk for cutaneous melanoma. /Sunscreens/[IARC Working Group on the Evaluation of Cancer-Preventive Agents (2001) Sunscreens (IARC Handbooks of Cancer Prevention, Vol. 5), Lyon, IARC; Unit of Chemoprevention: Cancer-Preventive Effects of Sunscreens.] **PEER REVIEWED**
  • SIGNS AND SYMPTOMS: Applications of 5% PABA in sunscreen formulation on human skin have shown that irritation is negligible.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**

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Non-Human Toxicity Excerpts

  • GENOTOXICITY: para-Aminobenzoic acid (1000 ug/mL) did not mutate Escherichia coli from streptomycin sensitivity to resistance or from histidine, methionine and tryptophan requirements to prototrophy (no liver activation was used in these experiments). The ethyl ester of para-aminobenzoic acid did not induce mutations in Salmonella typhimurium TA100 or TA98 in the presence or absence of a liver post-mitochondrial supernatant fraction from rats pretreated with polychlorinated biphenyl (Kanechlor 500) or phenobarbital, nor in E. coli WP2 in the absence of a rat liver preparation.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 256 (1978)] **PEER REVIEWED**
  • GENOTOXICITY: /Chinese hamster ovary cells (CHO)/ cultures in triplicate were incubated with PABA in solvent (DMSO), 8-MOP or MMS in culture flasks and incubated before irradiation. After treatment the cells were rinsed with buffer and grown for 18 hr. Afterwards chromosome preparations were made for the evaluation of chromosome aberrations and the mitotic index. In preliminary experiments the highest concentration of PABA, 1900 ug/mL, caused chromosome aberrations. This effect was enhanced by concomitant exposure to UVA/UVB.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • LABORATORY ANIMALS: Acute Exposure: ... In this study /researchers/ investigated the antioxidant effect of PABA in the cornea and lens of rats after its parabulbar injection. ... PABA in all studied concentrations essentially decreased the elevated levels of hydroperoxides and malonic dialdehyde and normalized catalase activity. The level of lipid peroxidation products and catalase activity normalized 24-28 hr after hypoxia, while after PABA it normalized within 2-11 hr. Antioxidant activity of emoxipin in the lens and cornea was the same as that of optimal antioxidant concentrations of PABA (0.02% for the cornea and 0.06% for the lens).[Akbervoa SI et al; Vestn Oftalmol 117(4):25-9 (2001)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Acute Exposure: ... PABA not only displays antithrombin activity, but also inhibits activated factor X and, upon intravenous injection to rats and rabbits, shows the antithrombotic effect. The most pronounced antithrombotic effect was observed at a dose of 1.5 mg/kg ... Equally efficient antithrombotic activity of blood plasma of rats was noted after intravenous injection of low molecular weight heparin "Fraxiparin" at 40 anti-Xa U/kg and PABA at 25 anti-Xa U/kg (1.5 mg/kg). ... The effect of PABA was expressed within 1.5 to 5 hr after injection with a peak of antithrombotic activity at 3 hr (which correlates with anti-IIa and anti-Xa activities of plasma) and terminated by 5 hr after injection.[Stroeva OG et al; Izv Akad Nauk Ser Biol Vol 3: 329-36 (1999)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Acute Exposure: Acute necrosis of the liver was found in dogs given 2-3 g/kg body weight para-aminobenzoic acid orally; acute gastroenteritis with hemorrhage was found in dogs given lethal doses.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 255 (1978)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Acute Exposure: Hairless mice /Female hairless (Hr/Hr) mice/ were exposed to UVB-irradiation in the presence or absence of PABA. PABA was applied on the back immediately before irradiation. MED was estimated. At the end of the study, the animals were killed, weighed and dorsal skin, left femoral lymph node and internal organs were sectioned and examined for tumors and metastases. In the unprotected groups (+/- vehicle) 100% of the animals were tumor-bearing, 90% were ... malignant tumors. In the protected groups, 12% of the animals were tumor-bearing, 4% were ... /malignant/ tumors. No animals in the non-irradiated groups developed tumors. The weight of the dorsal skin in the irradiated and protected group was significantly lower than in the irradiated and unprotected group. All cancers were squamous cell carcinoma (SCC) without metastases. No basal cell carcinoma (BCC) or melanomas were found.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • LABORATORY ANIMALS: Acute Exposure: The activating wavelengths for photocontact dermatitis were in long-wave ultraviolet light. The experimental photocontact sensitization was not induced in guinea pigs.[Horio T et al; Dermatologica 156 (2): 124-8 (1978)] **PEER REVIEWED** PubMed Abstract
  • LABORATORY ANIMALS: Chronic Exposure or Carcinogenicity: Groups of fifty 7 week old female Swiss mice received 0.02 mL of a 1, 5 or 10% solution of para-aminobenzoic acid in acetone applied to the dorsal skin twice weekly for up to 110 wk. A further group of 50 mice were painted with acetone alone, and 150 mice were left untreated. At 80 weeks, 23, 29 and 28 mice in the treated groups, 25 acetone treated controls and 82 untreated mice were still alive. The percentages of tumor bearing mice were 44% in acetone treated controls, 42% in untreated controls, and 36, 44 and 40% in the treated groups. Two acetone treated control mice, 3 untreated mice and 1 treated mouse had skin tumors. The incidences of lymphomas, lung adenomas and liver hemangiomas were similar in para-aminobenzoic acid treated and control mice.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 254 (1978)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Developmental or Reproductive Toxicity: ... Pregnant rats were injected intraperitoneally daily with 0.3% PABA at 5 mg/kg (0.3 mL/200 g): in group 2 during the preimplantation period (days 1-6 of pregnancy), in group 3 during the period of organogenesis (days 6-16), and in group 4 during days 1-16. In group 5, PABA was injected intraperitoneally (at 15 mg/kg (0.3 mL/200 g, three times a day) during days 6-16 of pregnancy and in group 6, intragastrically as a suspension at 50 mg/kg during days 1-16. ... Para-aminobenzoic acid at all tested doses does not exert a damaging effect and does not affect organogenesis. At doses 5 and 15 mg/kg, PABA does not affect growth but reduces the scattering of the extreme values of the parieto-coccygeal size and body mass.[Stroeva OG, Popov VB; Ontogenez 29(6): 444-9 (1998)] **PEER REVIEWED** PubMed Abstract
  • LABORATORY ANIMALS: Developmental or Reproductive Toxicity: Mice were given 50 mg/kg bw on days 9-11 /of gestation/. There was no increase in resorption frequency. However, a 23% resorption rate was reported in rats fed about 25 mg /p-aminobenzoic acid/ perkg bw. Rats received 1.0% /p-aminobenzoic acid/ in their diet before and during pregnancy. The treatment caused no adverse effects or malformations in newborns.[Sheftel, V.O.; Indirect Food Additives and Polymers. Migration and Toxicology. Lewis Publishers, Boca Raton, FL. 2000., p. 823] **PEER REVIEWED**
  • LABORATORY ANIMALS: Developmental or Reproductive Toxicity: Rats were mated and the percentage of resorptions after exposure to various antioxidants in the feed was determined. 29 compounds, among these PABA were tested. The number of resorptions was counted and the degree of resorption was recorded. The two horns of the uterus were examined separately. PABA caused 77.7% litters with resorptions and 23.8% of the implantations had terminated in resorption. Among the untreated pregnant rats, 40.8% had one or more resorptions and 10.6% of all recognized implantations had terminated in resorptions. Thus PABA caused both an increased number of resorptions in the single litter and an increased number of litters with resorptions.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • LABORATORY ANIMALS: Developmental or Reproductive Toxicity: Six female rats were fed diets containing 1% or 2% para-aminobenzoic acid from 23 to 60 days of age, at which time they were mated with males of proven fertility. No effects on reproduction or growth were observed.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 255 (1978)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Subchronic or Prechronic Exposure: ... PABA was provided at 0, 0.1, 0.5 and 1% in the drinking water for 4 weeks, during which the rats were fed a standard laboratory diet. The results showed that PABA affected neither the body weight gain nor the organ (liver, kidney, and spleen) weights during the 4-week period. The contents of PABA in the liver, kidney, and blood were increased in rats given 0.5% and 1% PABA in the water, whereas 0.1% PABA had little or no effect. The highest level of PABA achieved was 13 ug/g (95 nmol/g) and 5.1 ug/mL (37 nmol/mL) in the liver and blood, respectively, at week 4, and was 11 ug/g (80 nmol/g) in the kidney at week 2 after feeding began. Plasma aspartate aminotransferase activities in rats given 0.5% and 1% PABA were significantly lower than that of control rats at week 2, but not at week 1 or 4. Plasma alanine aminotransferase activities were not significantly affected by PABA. ... PABA, at 1% in the water, significantly decreased in vivo and in vitro (t-butylhydroperoxide-induced) lipid peroxidation in the liver but not in the kidney.[Chang TY , Miao-Lin H; J Nutr Biochem 7(7): 408-418 (1996)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Subchronic or Prechronic Exposure: ... After the first injection of 0.007% PABA, Interferon titer in the conjunctival washings was constantly increasing and reached the maximum after 48 hr (64-128 U/mL). Repeated injection of PABA after 5 days still more stimulated the production of Interferon, with the peak after 24 hr (128 U/mL); after 48 hr the titer of If was still high. ... after PABA the maximum Interferon titer (64 U/mL) was observed during the 4th and 12th hours postinjection and then decreased, remaining rather high after 24 hr. After 0.06% PABA, Interferon titers were 2-4 times lower in all experiments than after 0.007% PABA.[Akberova SI et al; Vestn Oftalmol 115(1): 24-6 (1999)] **PEER REVIEWED**
  • LABORATORY ANIMALS: Subchronic or Prechronic Exposure: Hairless mice /Female hairless (Hr/Hr) mice, 8 - 12 weeks old/ were exposed to UVB with or without protection with PABA or with photodegraded PABA daily for 30 weeks and were observed for a further 10 weeks. The effect was assessed as the development of tumor and the weight of dorsal skin. Tumor was defined as a papule >1x1x1 mm. The death rate of the animals was not significant in any group as compared to the control group. No animals in the non-irradiated groups developed cancer. All animals in the irradiated unprotected groups developed cancer. Protection with both pre-irradiated PABA (about 40% degradation) and non-irradiated PABA delayed the tumor induction time significantly compared to the unprotected groups. The mean weight of the dorsal skin of protected animals was lighter compared to the unprotected animals. All tumors registered were squamous cell carcinomas (SCC). Neither basocellular nor malignant melanomas were found. No metastases were found.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • LABORATORY ANIMALS: Subchronic or Prechronic Exposure: It was reported in an abstract that rats maintained on a synthetic diet containing 4% para-aminobenzoic acid for 2 mo exhibited moderated leucocytosis; of 40 day old rats maintained on the same diet containing 6% para-aminobenzoic acid, 63% died within a month, but no significant changes were observed in erythrocyte, leucocyte or platelet counts.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 255 (1978)] **PEER REVIEWED**

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Human Toxicity Values

  • None found

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Non-Human Toxicity Values

  • LD50 Dog oral 1000 mg/kg[Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 11th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2004., p. 152] **PEER REVIEWED**
  • LD50 Mouse oral 2850 mg/kg[Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 11th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2004., p. 152] **PEER REVIEWED**
  • LD50 Rabbit iv 2000 mg/kg[Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 11th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2004., p. 152] **PEER REVIEWED**
  • LD50 Rabbit oral 1830 mg/kg[Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 11th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2004., p. 152] **PEER REVIEWED**
  • LD50 Rat oral 6,000 mg/kg bw[Verschueren, K. Handbook of Environmental Data on Organic Chemicals. Volumes 1-2. 4th ed. John Wiley & Sons. New York, NY. 2001, p. 165] **PEER REVIEWED**

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Absorption, Distribution And Excretion

  • ... The transport of aminobenzoic acid across both the placenta and small intestine in rats was not consistent with its physicochemical properties. The compound crossed both barriers easily without any restrictions. Also, aminobenzoic acid was not widely distributed in rats.[Straud F et al; J Drug Target 5)(1): 57-65 (1997)] **PEER REVIEWED**
  • In a study with 4 volunteers, 93% PABA was recovered in the urine during the first 5 hours after a single oral dose of 80 mg PABA. In another study, 33 volunteers ingested 80 mg PABA in connection with meals. Mean urine recovery over a 24 hour period was 93+/-4% of the administered dose. With age of the volunteers a gradual delay in PABA recovery was observed. These studies show that PABA is absorbed rapidly from the gut, and that it is fast and almost completely eliminated with the urine within 24-hours.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • In one study performed with 40 healthy obstetric patients, procaine was injected into the mother at the time of delivering the baby. The doses ranged from 1 to 10 mg/kg bw. PABA is a metabolite of procaine and the biotransformation of procaine to PABA is rapid (in sec). The concentration of PABA found in the fetal circulation (the umbilical cord veins) was 40 - 60% as compared to the concentration in the maternal circulation. Thus, PABA can cross the placenta rapidly, but the transport mechanism still remains unknown. However, it is suspected that the mechanism for transport across the placental barrier is the same as for the intestine, i.e. carrier-mediated.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • Information on the cutaneous absorption, distribution, and elimination of most topically applied sunscreen agents is limited. Solvents used in sunscreen products affect the stability and binding of the drug to the skin; in general, alcoholic solvents allow for the most rapid and deepest epidermal penetration of sunscreens. It appears that sunscreen agents are absorbed by the intact epidermis to varying degrees. PABA reportedly diffuses into the stratum corneum, reaching maximum concentrations there 2 hours following application, but apparently does not penetrate deeper layers of the skin to a substantial extent. Homosalate's penetration also appears to be limited to the stratum corneum. One study in animals indicated that PABA may penetrate the skin to a greater extent than does padimate A. Although some studies have shown that substantive concentrations of PABA remain on the skin after washing, other studies have failed to confirm this. One study showed that PABA esters were removed from the skin less readily than was PABA or other chemical sunscreens.[American Society of Health-System Pharmacists 2013; Drug Information 2013. Bethesda, MD. 2013] **PEER REVIEWED**
  • It has been found that PABA is absorbed rapidly from the rat small intestine. The results indicate that PABA is transported through the intestine wall by a carrier-mediated transport system, and that the molecular structure of PABA is important for the absorption and its biotransformation characteristics.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • Of an oral dose of 1 g para-aminobenzoic acid, 82% was excreted in the urine of 3 male volunteers within 4 hr; para-aminohippuric acid and acetyl-para- aminohippuric acid were the principal metabolites. Concurrent administration of sodium benzoate totally abolished the excretion of these glycine conjugates.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 256 (1978)] **PEER REVIEWED**
  • Skin absorption of PABA corresponding to 1.6 to 9.6% of the applied amount of PABA was measured in the urine of six male volunteers after application of PABA in three different preparations. No significant difference where observed between the three preparations.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • Solvents used in sunscreen products affect the stability and binding of the drug to the skin; in general, alcoholic solvents allow for the most rapid and deepest epidermal penetration of sunscreens. It appears that sunscreen agents are absorbed by the intact epidermis to varying degrees. /Sunscreens/[American Society of Health-System Pharmacists 2013; Drug Information 2013. Bethesda, MD. 2013] **PEER REVIEWED**
  • The percutaneous absorption and metabolism of three structurally related compounds, benzoic acid, p-aminobenzoic acid (PABA), and ethyl aminobenzoate (benzocaine), were determined in vitro through hairless guinea pig skin. Benzocaine was also studied in human skin. Absorption of benzocaine was rapid and similar through both viable and nonviable skin. The absorption of the two acidic compounds, benzoic acid and PABA, was greater through nonviable skin. A small portion (6.9%) of absorbed benzoic acid was conjugated with glycine to form hippuric acid. Although N-acetyl-benzocaine had not been observed as a metabolite of benzocaine when studied by other routes of administration, both PABA and benzocaine were extensively N-acetylated during percutaneous absorption. Thus, the metabolism of these compounds should be considered in an accurate assessment of absorption after topical application.[Nathan D et al; Pharm Res 7(11): 1147-51(1990)] **PEER REVIEWED** PubMed Abstract
  • The toxicokinetics of PABA is characterized by fast oral absorption, biotransformation by the major routes acetylation and glycine conjugation, the minor route by glucuronidation in the liver and kidney, and a fast and almost complete elimination via the urine within 24 hrs. PABA is extensively acetylated during percutaneous absorption in humans. Studies have shown that PABA can cross the placenta rapidly. Furthermore, the results of one study indicate that the human placenta has a significant capacity for acetylation of PABA.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**

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Metabolism/Metabolites

  • ... PABA is predominantly metabolized by acetylation and glycine conjugation to form p-acetamidobenzoic acid (PAABA), p-aminohippuric acid (PAHA), and p-acetamidohippuric acid (PAAHA). ... The half-lives of PABA were 7.01 +/- 0.32 min in rapid acetylation rabbits and 7.08 +/- 0.78 min in slow acetylation rabbits. Significant differences were obtained in formation of PAABA and PAHA formed from PABA in both acetylation phenotype rabbits.[Song DJ et al; Biopharm Drug Dispos 20(5): 263-270 (1999)] **PEER REVIEWED** PubMed Abstract
  • A study with rabbits showed that PABA administrated intravenously was excreted mainly as the acetyl conjugate, p-acetamidobenzoic acid. Smaller amounts of p-aminohippuric acid and p-acetamidohippuric acid were also formed. The p-aminohippuric acid, formed by conjugation with glycine can be further acetylated to p-acetamidohippuric acid. In rabbits, 30-40% of the acetylation to p-acetamidobenzoic acid occurred in the kidney. Human studies have shown that PABA is being biotransformed primarily by acetylation and glycine conjugation and in smaller amounts by glucuronidation.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • Acetylation is dose-dependent. In rats given up to 5 mg/kg bw, 75% of the metabolites were acetylated; with higher doses, the extent of acetylation decreased down to 40%. An inverse relationship exists between acetylation and glycine conjugation: when acetylation decreases, glycine conjugation increases; such a decrease is seen in pantothenic acid-deficient rats. . Male rats excreted a larger amount of acetylated conjugates in the urine than females.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 255 (1978)] **PEER REVIEWED**
  • After oral doses of 500 mg para-aminobenzoic acid, 88% of the metabolites are acetylated; this fraction decreases with higher doses, glycine conjugation is low in the newborn. para-Aminobenzoic acid is acetylated by homogenates of human placenta.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 256 (1978)] **PEER REVIEWED**
  • Although N-acetyl-benzocaine had not been observed as a metabolite of benzocaine when studied by other routes of administration, both PABA and benzocaine were extensively N-acetylated during percutaneous absorption. Thus, the metabolism of these compounds should be considered in an accurate assessment of absorption after topical application.[Nathan D et al; Pharm Res 7(11): 1147-51(1990)] **PEER REVIEWED** PubMed Abstract
  • Following ingestion /in man/ of 1.0 g, ...main metabolites were p-aminohippuric acid and acetyl-p-aminohippuric acid.[Sheftel, V.O.; Indirect Food Additives and Polymers. Migration and Toxicology. Lewis Publishers, Boca Raton, FL. 2000., p. 823] **PEER REVIEWED**
  • N-Acetyltransferases (NAT) are important enzymes in the metabolism of certain carcinogenic arylamines, as N-acetylation decreases or prevents their bioactivation via N-hydroxylation. To study such processes in the bladder, cell culture models may be used, but metabolic competence needs to be characterized. This study focused on the N-acetylation capacity of two urothelial cell systems, using p-aminobenzoic acid (PABA) and the hair dye precursor p-phenylenediamine (PPD), two well-known substrates of the enzyme NAT1. The constitutive NAT1 activity was investigated using primary cultures of porcine urinary bladder epithelial cells (PUBEC) and in the human urothelial cell line 5637 to assess their suitability for further in vitro studies on PABA and PPD-induced toxicity. N-Acetylation of PABA and PPD was determined by high-performance liquid chromatography (HPLC) analysis in cytosols of the two cell systems upon incubation with various substrate levels for up to 60 min. The primary PUBEC revealed higher N-acetylation rates (2.5-fold for PABA, 5-fold for PPD) compared to the 5637 cell line, based on both PABA conversion to its acetylated metabolite and formation of mono- and diacetylated PPD. The urothelial cell systems may thus be useful as a tool for further studies on the N-acetylation of aromatic amines via NAT1.[Follmann W et al; J Toxicol Environ Health A. 75 (19-20):1206-15 (2012)] **PEER REVIEWED** PubMed Abstract
  • PABA is extensively acetylated on the primary amino group during percutaneous absorption in the hairless guinea pig and human.[European Commission Scientific Committeee on Consumer Products; Opinion on 4-Aminobenzoic acid (PABA), Available from, as of October 18, 2013: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf] **PEER REVIEWED**
  • The two major metabolic pathways in a variety of species (guinea-pigs, rabbits and rats, but not dogs) are acetylation of the amino group and conjugation of the carboxy group, either with glycine or with glucuronic acid. Acetylation occurs in liver, heart, lung, blood and kidneys of rats and in the mucous membranes of the gastrointestinal tract of cattle. N-Acetyl-transferase activity in the presence of para-aminobenzoic acid is similar in liver and lung tissue of rabbits. Acetylation not only of para-aminobenzoic acid (30-40%) but also of para-aminohippuric acid (70%) takes place in the kidney of rabbits; acetylation of para-aminohippurate also occurs in the kidney of guinea-pigs.[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: http://monographs.iarc.fr/ENG/Classification/index.php, p. V16 255 (1978)] **PEER REVIEWED**

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Tsca Test Submissions

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Footnotes

1 Source: the NTP's CEBS database.

2 Source: the National Library of Medicine's Hazardous Substance Database, 02/28/2017.

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