How do chemicals cause skin depigmentation or skin hypopigmentation?

Monobenzyl ether of hydroquinone (MBEH) and para–substituted phenols (PSP) cause skin depigmentation by destroying melanocytes. It is believed that both MBEH and PSP are taken up by melanocytes and metabolized into toxic products that kill the melanocytes. Hydroquinone, a commonly used skin-lightening agent, causes decreased melanin synthesis by competing with tyrosine and dihydroxyphenylalanine for the enzyme tyrosinase. With hydroquinone bound to its active site, tyrosinase is unable to synthesize melanin. Other chemicals, such as arsenic, mercaptoethyl amines, chloroquine, hydroxychloroquine, and corticosteroids, act to metabolically suppress melanocytes, resulting in decreased melanin synthesis and skin lightening. In most cases, the effects of these chemicals are reversible.