Para-aminobenzoic acid, also known as 4-aminobenzoic acid and PABA, is a natural substance often included in sunscreen products and other skin care items. It also shows some potential as an oral supplement. Sometimes, people refer to PABA as "vitamin Bx," but it is not a true vitamin, according to the U.S. National Institutes of Health on its MedlinePlus website. Consult with a qualified health care provider before taking PABA supplements, because taking large doses can cause harmful side effects.
PABA is not considered an essential nutrient, as noted by the Beth Israel Deaconess Medical Center, or BIDMC. It is usually present in supplements that contain B vitamins, because it is a component of folic acid, or vitamin B-9. PABA is found in Brewer's yeast, beef liver and other meat, eggs, milk, mushrooms, spinach, whole grains and molasses.
When applied to the skin, PABA physically blocks rays from ultraviolet light, explains the BIDMC. This prevents sunburn and protects skin from other harmful effects of the sun, such as gradually occurring areas of skin discoloration and changes in texture, and the increased risk of skin cancer.
Some medicinal uses for oral PABA supplements have also been proposed, according to the BIDMC. These include treating diseases of the skin and connective tissue, male infertility, and Peyronie's disease, in which the penis becomes bent due to a build-up of fibrous plaque. A study cited by the BIDMC found that men with Peyronie's disease who took 3 grams of PABA four times per day experienced significant slowing of disease progression, but the supplement did not decrease the existing plaque.
A common therapeutic dosage of oral PABA is 300 to 400 milligrams per day, according to the BIDMC, but participants in some studies have taken much higher dosages. The BIDMC recommends not taking more than 400 milligrams per day unless you have a medical recommendation to do so. You can obtain small amounts of PABA, such as 25 milligrams, by taking multivitamins or B-complex vitamins. PABA supplements are available in single doses as high as 1,000 milligrams, according to physician and natural supplement expert Ray Sahelian.
PABA is probably safe if taken at a dosage of 400 milligrams per day or less, according to the BIDMC. Side effects associated with this dosage include loss of appetite and skin rash. Vitiligo, a skin disorder involving light patches and uneven pigmentation, has occurred with PABA dosages above 8 grams per day. One woman developed liver toxicity while taking 12 grams per day, as noted by the BIDMC, but she recovered completely after discontinuing the supplement.