Para-aminobenzoic acid (PABA) is a naturally occurring nonprotein amino acid. Although early studies suggested that PABA was a B vitamin, PABA is now known to be neither a vitamin nor an essential nutrient. Although dietary PABA deficiency is not an issue in humans, PABA is found in foods such as liver, kidney, wheat germ, bran, and yogurt. Sulfonamide antibiotics interfere with the reproduction of some bacteria by interfering with PABA conversion into folic acid, the latter of which is required for DNA synthesis.
Historical uses of PABA included treatment of hair loss and restoration of color to graying hair, with variable effectiveness. PABA first emerged as a sunscreen after World War II due to its ability to absorb ultraviolet B light. However, it was soon recognized that PABA was a "sensitizer" and stimulated allergic reactions. PABA was also suspected of being a causative agent in several autoimmune diseases. Consequently, PABA gradually ceased to be used in sunscreens, which were then marketed as being "PABA free."
PABA has also been used in a variety of diagnostic laboratory tests and as a structural component of many drugs. PABA has shown promise as a potential treatment for melasma. Melasma is a darkening of the skin in sun-exposed areas of the body, particularly the face. When melasma occurs in pregnant women, it is known as "the mask of pregnancy." PABA has also shown promise in the treatment of inflamed corneas associated with a herpes virus infection and in the prevention of recurrent herpes infections that cause sores on the mouth, lips, and gums.
2,3,5,6-Tetrafluorophenyl n-(s-benzoylthioacetyl)glycylglycyl-p-aminobenzoate, 4-aminobenzoic acid, 4-aminobenzoic acid hydrazide, ABAH, Actipol®, Aktipol®, aminobenzoate potassium, aminobenzoic acid, BAB, BT-PABA, buytl aminobenzoate, cyclic amino acid, disulfate ester of ursodeoxycholyl-p-aminobenzoic acid, disulphate ester of ursodeoxycholyl-p-aminobenzoic acid, ester oxybenzone, ethyl p-aminobenzoate, ethyl dihydroxypropylaminobenzoate, glyceryl para-aminobenzoate, KPAB, K-para-aminobenzoate, monoglyceryl para-aminobenzoate, n-benzyol-l-tyrosyl-p-aminobenzoic acid, NBT-PABA, n-butyl-p-aminobenzoate, n-diethyl-methyl-ammonium ethyl bromide-p-[2(n-octyloxy)-benzoyl-]aminobenzoate, octyl dimethyl PABA, PABA ester, Pabafil®, PABA-UDCA, padimate O, PAMBA, p-aminobenzoic acid, para aminobenzoic acid, para-aminobenzoate, para-aminobenzoate potassium, paraaminobenzoic acid, para-aminobenzoic acid, para-aminomethylbenzoic acid, PEG-25 PABAs, Peptide-PABA, Photoplex, POTABA®, potassium para-aminobenzoate, synthetic peptide Bz-Ty PABA, UDCA-PABA, ursodeoxycholic acid-p-aminobenzoic acid, vitamin Bx, vitamin H.
Metabolites: Para-acetoamidobenzoic acid (PAABA), para-acetamidohippuric acid (PAAHA), para-aminohippuric acid (PAHA).
Derivatives of PABA commonly used for therapeutic purposes: BAB (butyl aminobenzoate, for epidural injection), KPAB (potassium para-aminobenzoate, for taking by mouth), padimate O (PABA ester, for use on the outside of the body), PAMBA (para-aminomethylbenzoic acid, for taking by mouth or intramuscular use).
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Actipol® is a 0.007% PABA solution for eye use that has been studied for the treatment of inflamed corneas caused by the herpes virus. The solution has been found to be effective in curing most patients. Further studies may provide additional useful information on the use of PABA for this condition.
Preliminary data suggest that PABA may be effective in the prevention of melasma (also known as chloasma) in pregnant women. Melasma is a darkening of the skin on sun-exposed areas of the body, particularly the face. When melasma occurs in pregnant women, it is known as "the mask of pregnancy." Additional studies are needed before a conclusion can be made.
Recurrent herpes labialis infection (prevention)
Sun exposure has been shown to stimulate the reactivation of a herpes simplex virus infection on the lips, as well as in the mouth or gums. Limited research suggests that PABA in sunscreen may be effective in preventing recurrent herpes labialis. Further studies will provide additional useful information on the use of PABA for this condition.
Preliminary evidence suggests that para-aminomethylbenzoic acid (PAMBA; a PABA derivative that is taken by mouth or injected into muscle) may help prevent worsening of asthma symptoms following a bronchoprovocation challenge (a test to determine whether a patient has asthma). Further studies are needed before a conclusion can be made.
Autoimmune disorders (pemphigus vulgaris adjuvant)
Preliminary data suggest that para-aminomethylbenzoic acid (PAMBA; a PABA derivative that is taken by mouth or injected into muscle) might allow patients with the autoimmune blistering disease pemphigus vulgaris to reduce their steroid dosage. Additional studies are needed in this area.
The PABA derivative n-butyl-p-aminobenzoate (BAB) can be injected into the epidural space of the spine and used as a local anesthetic. Preliminary data suggest that BAB treatment may provide significant pain relief to cancer patients who are experiencing pain that is difficult to manage. Further research is necessary before a conclusion can be made.
Preliminary evidence suggests that a combination product containing PABA (Pantogar®; containing PABA, B vitamins, calcium-d-pantothenate, vigar yeast, L-cystine, and keratin) may be effective in the treatment of hair loss. Further research on the effect of PABA alone is needed.
Inflammatory skin disorders (lichen sclerosus)
Limited research suggests that potassium para-aminobenzoate (KPAB; a PABA derivative taken by mouth) may be effective in the treatment of lichen sclerosus, a skin condition that is characterized by inflammation, itching, and pain, particularly in the anogenital area. Additional research is needed in this area.
Limited research suggests that potassium para-aminobenzoate (KPAB; PABA derivative taken by mouth) may improve the symptoms of Peyronie's disease. Peyronie's disease is a connective tissue disorder that primarily affects the penis, causing pain, curvature of the penis, and sexual dysfunction. Additional studies are needed before a conclusion can be made.
Studies investigating the use of potassium para-aminobenzoate (KPAB; a PABA derivative taken by mouth) as a treatment for skin changes in scleroderma have shown mixed results. Further high-quality research is needed to determine if PABA may be useful in the treatment of this condition.
PABA was best known for its use as a component of sunscreen products for the skin. However, there are few studies demonstrating its effectiveness for this purpose. The use of PABA in sunscreen has been reduced due to the reportedly high frequency of allergic reactions and cross-sensitivity with other medications. Further studies may help to better characterize the sun-protective properties of PABA.