5- Tretinoin: Tretinoin is the main topical retinoid that has been used in skin whitening products. The mechanisms for reducing pigmentation include inhibition of tyrosinase induction, interference with pigment transfer, and acceleration of epidermal turnover.
They also have the ability to disperse pigment granules within keratinocytes. Retinoids may act as penetration enhancers when used with other whitening agents like hydroquinone and mequinol.
The most common adverse effects include burning, stinging, erythema, dryness, and scaling.
Although the adverse effects are reversible, retinoid dermatitis may itself lead to hyperpigmentation, especially in dark-skinned individuals (Policarpio and Lue, 2009).