Irritation was a common side effect which resolved with the temporary cessation of application and application of moisturizers. [36] Mequinol Mequinol (4-hydroxyanisole, hydroquinone monomethyl ether) is a derivative of HQ. Its mechanism of action is unclear; however, being a substrate of tyrosinase, it may act as a competitive inhibitor of the formation of melanin precursors [11] .