How can you treat the skin darkened due to allergy?

Not allergy: One may have darkened skin from scratching leading to overpigmentation but allergic skin conditions (atopic ezcema, allergic contact dermatitis etc) per se does not cause darkened skin. On the flip side, too much scratching may also lead to loss in melanin on the skin leading to a white area called vitiligo. First thing, stop scratching. Rx bleaching cream may help to lighten up the darken area.