4-Hydroxybenzoic acid is primarily known as the basis for the preparation of its esters, known as parabens, which are used as preservatives in cosmetics and some ophthalmic solutions.

It is found in plants of the genus Vitex such as V. agnus-castus or V. negundo, and in Hypericum perforatum (St John's wort).

The compound is also found in Ganoderma lucidum, a medicinal mushroom with the longest record of use.

[3] It is one of the main catechins metabolites found in humans after consumption of green tea infusions.

[4] It is also found in wine,[5] in vanilla, in Macrotyloma uniflorum (horse gram), carob[6] and in Phyllanthus acidus (Otaheite gooseberry).

[citation needed] p-Hydroxybenzoic acid glucoside can be found in mycorrhizal and non-mycorrhizal roots of Norway spruces (Picea abies).

[8] Violdelphin is an anthocyanin, a type of plant pigments, found in blue flowers and incorporating two p-hydroxybenzoic acid residues, one rutinoside and two glucosides associated with a delphinidin.

This enzyme catalyses the first step in ubiquinone biosynthesis in Escherichia coli and other Gram-negative bacteria.

[10] The enzyme 4-methoxybenzoate monooxygenase (O-demethylating) transforms 4-methoxybenzoate, an electron acceptor AH2 and O2 into 4-hydroxybenzoate, formaldehyde, the reduction product A and H2O.

Biosynthetically, alkannin is produced in plants from the intermediates 4-hydroxybenzoic acid and geranyl pyrophosphate.

It is known to metabolize aromatic compounds of low molecular weight, such as p-hydroxybenzoic acid.

4-Hydroxybenzoic acid is produced commercially from potassium phenoxide and carbon dioxide in the Kolbe-Schmitt reaction.

[citation needed] Its acid dissociation follows this equation: Vectran is a manufactured fiber, spun from a liquid crystal polymer.

The fiber has been shown to exhibit strong radiation shielding used by Bigelow Aerospace and produced by StemRad.

Examples of drugs made from PHBA include nifuroxazide, orthocaine, ormeloxifene and proxymetacaine.

[14] 4-Hydroxybenzoic acid has estrogenic activity both in vitro and in vivo,[15] and stimulates the growth of human breast cancer cell lines.