Para-aminobenzoic acid (PABA) is best known as the active ingredient in sunblock. This use of PABA is not really medicinal: like a pair of sunglasses, PABA physically blocks ultraviolet rays when it is applied to the skin.

There are, however, some proposed medicinal uses of oral PABA supplements. PABA is sometimes suggested as a treatment for various diseases of the skin and connective tissue, as well as for male infertility. However, most of the clinical data on PABA comes from very old studies, some from the early 1940s.



PABA is not believed to be an essential nutrient. Nonetheless, it is found in foods, mainly in grains and meat. Small amounts of PABA are usually present in B vitamin supplements as well as in some multiple vitamins.

Therapeutic Dosages

A typical therapeutic dosage of PABA is 300 to 400 mg daily. Some studies have used much higher dosages. However, serious side effects have been found in dosages above 8 g daily (see Safety Issues). You probably shouldn’t take more than 400 mg daily except on medical advice.

Therapeutic Uses

PABA has been suggested as a treatment for Peyronie's disease]]> , a condition in which the penis becomes bent owing to the accumulation of fibrous plaques ]]>4–6]]> However, there has been only one reported double-blind placebo-controlled study properly examining this use. (For information on why such studies are essential, see ]]>Why Does This Database Rely on Double-Blind Studies?]]> ) This trial enrolled 103 men with Peyronie's disease and followed them for one year. The results showed that use of PABA at a dose of 3g 4x daily significantly slowed the progression of Peyronie’s disease; it did not, however, reduce pre-existing plaque.

PABA has also been suggested as a treatment for ]]>scleroderma]]> , a disease that creates fibrous tissue in the skin and internal organs. ]]>1,2]]> A 4-month ]]>double-blind, placebo-controlled]]> study of 146 people with long-standing, stable scleroderma did not support this, failing to find any evidence of benefit. ]]>3]]> However, half the participants in this trial dropped out before the end, making the results unreliable.

Based on one small World War II–era study, PABA has been suggested for treating ]]>male infertility]]> as well as ]]>vitiligo]]> , a condition in which patches of skin lose their pigment, resulting in pale blotches. However, this study didn't have a control group, so its results aren't meaningful. ]]>7]]> Ironically, a recent study suggests that high dosages of PABA can cause vitiligo (see Safety Issues).


Safety Issues

PABA is probably safe when taken at a dosage up to 400 mg daily. Possible side effects at this dosage are minor, including skin rash and loss of appetite. 8]]>

Higher doses are a different story, however. There has been one reported case of severe liver toxicity in a woman taking 12 g daily of PABA. ]]>9]]> Fortunately, her liver recovered completely after she discontinued her use of this supplement. Also, a recent study suggests that 8 g daily of PABA can cause vitiligo, the patchy skin disease described previously. ]]>10]]>

Clearly, there are questions that need to be answered about the safety of high-dose PABA therapy. You shouldn’t take more than 400 mg daily except under medical supervision.

PABA may interfere with certain medications, including ]]>sulfa antibiotics]]> . ]]>11,12]]>

Safety in young children, pregnant or nursing women, or those with serious liver or kidney disease has not been determined.


Interactions You Should Know About

If you are taking sulfa antibiotics]]> such as ]]>Bactrim]]> or ]]>Septra]]> , do not take PABA supplements except on medical advice.