Mequinol

Mequinol, MeHQ or 4-methoxyphenol, is an organic compound with the formula CH3OC6H4OH. It is a phenol with a methoxy group in the para position. A colorless solid, it is used in dermatology and organic chemistry.

Use in dermatology
Mequinol is a common active ingredient in topical drugs used for skin depigmentation. As a topical drug mequinol is often mixed with tretinoin, a topical retinoid. A common formulation for this drug is an ethanolic solution of 2% mequinol and 0.01% tretinoin by mass. Dermatologists commonly prescribe the drug to treat liver spots.

Lower dosages of mequinol have been used in conjunction with a Q-switched laser to depigment skin in patients with disseminated idiopathic vitiligo.

Organic chemistry
In organic chemistry 4-methoxyphenol is used as a polymerisation inhibitor (e.g. acrylates or styrene monomers).

4-Methoxyphenol can be produced from p-benzoquinone and methanol via a free radical reaction.

Safety
The U.S. National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday.