4-Aminobenzoic acid

Overview
4-Aminobenzoic acid (also known as para-aminobenzoic acid or PABA) is an organic compound with the molecular formula C7H7NO2. PABA is a white crystalline substance that is only slightly soluble in water. It consists of a benzene ring substituted with an amino group and a carboxylic acid.

Organic
PABA is an essential nutrient for some bacteria and is sometimes called Vitamin Bx. However, PABA is not essential to human health, and is therefore not officially classified as a vitamin. Although humans lack the ability to synthesize folate from PABA, it is sometimes marketed as an essential nutrient under the premise that it can stimulate intestinal bacteria.

PABA is an intermediate in bacterial synthesis of folate. Sulfonamides are chemically similar to PABA, and their antibacterial activity is due to their ability to interfere with conversion of PABA to folate by dihydropteroate synthetase, and subsequent utilization, by bacteria.

Industrial
In the past, PABA has been widely used as a UV filter in sunscreen formulations. However, there have been inconclusive studies on whether it increases the formation of a particular DNA defect in human cells, thus increasing the risk of skin cancer. Currently, safer and more effective derivatives of PABA, such as octyl dimethyl PABA, are more commonly used.

The potassium salt is used as a drug against fibrotic skin disorders under the trade name POTABA. PABA is also occasionally used in pill form by sufferers of Irritable bowel syndrome to treat the associated gastrointestinal symptoms.

PABA also finds use in the manufacture of esters, folic acid, and azo dyes.