the fact of some areas of skin being darker than others, often caused by skin damage or certain medical conditions

Hyperpigmentation may be caused by certain drugs. 某些药物可能会引起色素沉着过度。

Freshly waxed skin is prone to hyperpigmentation if it's not protected with sunscreen. 刚打过蜡的皮肤如果没有防晒霜的保护，很容易出现色素沉着过度。