Background

• 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.

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