Phenol

Phenol is an antimicrobial preservative used to extend a product's shelf life by inhibiting the growth of bacteria and mold. It's most commonly found in lip care, cleansers, and treatments at concentrations of 1–2%, and can also function as a denaturant, deodorant, or fragrance ingredient.

Unlike most cosmetic preservatives, phenol can damage skin at the concentrations typically used in products. Research has identified roughly 1.5% as the threshold at which phenol begins to cause skin damage - sitting within the range it's normally formulated at.

It works by denaturing proteins, which is what gives it both its antimicrobial activity and its potential to cause chemical burns, redness, peeling, or stinging. Phenol also has a mild local anesthetic effect, so irritation may not be felt right away even when damage is occurring. The lips and other thin-skinned areas are especially susceptible.

The use of phenol in cosmetics is prohibited in the European Union and Canada. In the United States, it remains permitted primarily in OTC drug products such as oral analgesics and medicated lip balms.