Mask of pregnancy: Muddy-brown pigmentation on the cheeks or elsewhere on the face that develops in about half of all women during pregnancy. Some women also develop it outside pregnancy, as do some women on hormone therapy. The pigmentation is worsened by ultraviolet (UV) light, which tends to darken it. Regular use of a broad-spectrum sunscreen against both UVA and UVB can prevent progression of the condition. The hyperpigmentation (excess pigment in the skin) usually lightens up with the use of topical treatment with bleaching agents, together with the topical application of retinoin (vitamin A acid, Retin-A). Light chemical peels can also aid and abet the effects of the topical therapy. Also known as melasma or chloasma.