Para-Aminobenzoic Acid (PABA) Encyclopedia — Scientific Background

What Is Para-Aminobenzoic Acid?

Para-aminobenzoic acid (PABA, CAS 150-13-0), also known as 4-aminobenzoic acid, p-aminobenzoic acid, or vitamin B10, is an organic compound with the molecular formula C₇H₇NO₂ and a molecular weight of 137.14 g/mol. It is an aminobenzoic acid in which the amino group is para to the carboxy group. PABA is a white crystalline solid, although commercial samples can appear gray, and it is only slightly soluble in water. The pure substance crystallizes in colorless needles which upon ageing, particularly under the influence of air and light, acquire a yellowish cast. PABA was first synthesized in 1863 by reduction of 4-nitrobenzoic acid with ammonium sulfide.

Physiological Functions of PABA

PABA was historically classified as a member of the vitamin B complex and was known as vitamin B10 or vitamin BX. While it is not considered a true vitamin for humans (since humans cannot synthesize folate from PABA), it serves several important physiological functions:

• Folate Biosynthesis Precursor — PABA is a precursor in the biosynthesis of folate (vitamin B9) in bacteria and plants, and is a structural component of folic acid and certain coenzymes. In humans, PABA is a byproduct of tryptophan metabolism and also plays an active role in various biological processes.

• Neurotransmitter Synthesis Modulation — Experimental and clinical evidence demonstrates that PABA enhances serotonin and dopamine synthesis by activating key enzymes including tryptophan hydroxylase and tyrosine hydroxylase, thereby stabilizing mood and improving cognitive function.

• Antioxidant Defense — PABA scavenges reactive oxygen species (ROS) to mitigate oxidative stress and protect cellular integrity.

• Anti-Inflammatory Activity — PABA suppresses neuroinflammation by inhibiting NF-κB signaling and cytokine production (including IL-1β and TNF-α).

• Skin and Hair Support — PABA has been historically used to support skin health and hair pigmentation. Research has shown that PABA may have the potential to aid skin-related disorders. PABA seems to be beneficial to maintain healthy hair by reducing hair loss and decreasing greying of hair in both men and women.

Mechanisms of Action

Neurotransmitter Modulation — Serotonin and Dopamine Synthesis

PABA exhibits multifaceted therapeutic potential in neuropsychiatric disorders through its roles in neurotransmitter modulation. Experimental and clinical evidence demonstrates that PABA enhances serotonin and dopamine synthesis by activating key enzymes including tryptophan hydroxylase (the rate-limiting enzyme in serotonin synthesis) and tyrosine hydroxylase (the rate-limiting enzyme in catecholamine synthesis). This dual activation mechanism supports mood stabilization and cognitive function.

Anti-Inflammatory and Antioxidant Pathways

PABA suppresses neuroinflammation by inhibiting NF-κB signaling and cytokine production, including IL-1β and TNF-α. It also scavenges reactive oxygen species (ROS) to mitigate oxidative stress and protect neuronal integrity. This dual anti-inflammatory and antioxidant activity makes PABA a potential neuroprotective agent.

Synergy with Traditional Antidepressants

Clinical studies indicate that PABA may synergize with traditional antidepressants by targeting serotonin reuptake transporters (SERT) and monoamine oxidase (MAO), offering improved outcomes in major depressive disorder.

Folate Synthesis and One-Carbon Metabolism

PABA is a structural component of folic acid and certain coenzymes. In bacteria and plants, PABA is a precursor in the biosynthesis of folate, which is essential for one-carbon metabolism, nucleotide synthesis, and amino acid metabolism.

Clinical Evidence

Hair Pigmentation — Clinical Study

A study of 460 patients with gray hair who took 100 mg of PABA three times a day led to pigment restoration within 2–4 months in 82% of patients. Zarafonetis reported hair repigmentation with doses of 12–20 g of PABA, though these high doses are no longer recommended due to safety concerns. Temporary hair darkening has been noted in individuals ingesting significant amounts of PABA.

Scleroderma — Retrospective Study

A retrospective study in 467 people with scleroderma showed that PABA supplementation was associated with skin-softening effects. The potassium salt of PABA is used therapeutically in fibrotic skin disorders.

Neuropsychiatric Disorders — Comprehensive Review

A comprehensive review published in Exploration of Drug Science (2025) examined the molecular mechanisms and therapeutic prospects of PABA in neuropsychiatric disorders. The review concluded that PABA exhibits multifaceted therapeutic potential through neurotransmitter modulation, anti-inflammatory action, and antioxidant defense, and called for further research to optimize dosing regimens, validate long-term safety, and explore pharmacogenomic interactions.

Dermatitis Herpetiformis

PABA in high amounts has been reported to reduce or eliminate the skin lesions of dermatitis herpetiformis (DH) in one preliminary trial.

The Bioavailability Challenge

Despite its biological activities, native PABA presents significant formulation challenges. The compound is only slightly soluble in water, with one part dissolving in approximately 200 parts of water at room temperature, and it is rapidly cleared by the kidneys following oral administration. PABA is metabolized to para-aminohippuric acid and excreted primarily in the urine.

liposomal encapsulation addresses these limitations through a phospholipid bilayer that protects PABA during digestive transit and facilitates enhanced intestinal absorption. Liquid crystal-drug formulations of PABA have demonstrated significantly improved bioavailability compared to PABA solution alone. Liposomal PABA forms a stable dispersion in aqueous systems, suitable for functional beverages and liquid formulations.

Liposomal PABA

Liposomal encapsulation of PABA provides a fundamentally different delivery mechanism from conventional forms. The phospholipid bilayer surrounds the PABA molecule, forming a protective shell that enhances solubility, stability, and cellular uptake. This delivery system:

• Improves aqueous dispersibility of PABA

• Protects PABA from oxidative degradation and discoloration

• Enhances intestinal absorption through lipid-mediated pathways

• Provides sustained release for prolonged biological activity

Safety and Regulatory

PABA has a complex safety and regulatory profile that requires careful consideration:

Dose-Dependent Toxicity: Ingestions of more than 10 grams per day for days have been necessary to induce symptoms other than local gastrointestinal irritation. Clinical use of PABA at doses of 10 grams per day or more have produced nausea, vomiting, acidosis, pruritus, rash, fever, methaemoglobinemia and, possibly, hepatitis. A daily dose of more than 12 g was reported to be unsafe and can bring about serious side effects such as liver, kidney, and blood problems. Two case reports indicate hepatic injury after oral intake of PABA in doses of 12 g/day, corresponding to 200 mg/kg body weight for a human of weight 60 kg.

Sunscreen Use — FDA Regulatory Action: In 2026, the FDA issued a final administrative order amending the Over-the-Counter Monograph M020 to remove PABA as a sunscreen active ingredient. A sunscreen drug product containing PABA is not generally recognized as safe and effective (GRASE). The FDA has proposed that PABA is no longer a safe ingredient in sunscreens because of the risk of allergic skin reactions and because it can make skin more sensitive to sunlight. This regulatory action applies specifically to sunscreen drug products and does not affect PABA's status as a dietary supplement ingredient when used orally.

EU Cosmetics Regulation: PABA is listed as a prohibited cosmetic ingredient in the European Union (II/167).

Dietary Supplement Status: PABA is commercialized as a dietary supplement ingredient in the United States. The FDA has proposed that PABA is not generally recognized as safe (GRAS) for use as a sunscreen active ingredient, but this does not preclude its use as a dietary supplement ingredient at appropriate doses.

Animal Toxicity Data: Rats are resistant to orally administered PABA and tolerate 1.4 g/kg body weight for about a month. A NOAEL of greater than 1.4 g/kg body weight was established in a 28-day oral toxicity study in rats.

Precautions: Individuals with known hypersensitivity to PABA or related compounds (including sulfonamides and benzocaine) should avoid supplementation. PABA may interact with sulfonamide antibiotics and should not be used concurrently without medical supervision. Pregnant or lactating women and children should consult a healthcare professional before use. High doses of PABA may interfere with thyroid function tests and liver function tests.

Testing protocols must adhere to international standards including USP, European Pharmacopoeia, and FAO/WHO Codex Alimentarius. Formulators should verify local regulatory requirements prior to market entry.

This product is intended for research, nutraceutical, and functional food applications. Not intended to diagnose, treat, cure, or prevent any disease.

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