Pityriasis alba, vitiligo, tsc?

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Different conditions. These conditions can present with lightening or "hypopigmentation" of the skin but they have different causes. Pityriasis alba is form of eczema and vitiligo is an autoimmune process by which your body attacks the pigment producing cells called melanocytes which leads to loss of pigment. Not sure what tsc is, but lsc stands for lichen simplex chronicus:changes caused by rubbing/scratching skin.