Allergy acne is mainly flaky red spots or appear as dense bumps, medically known as papules. The common causes are contact dermatitis, urticaria, eczema and so on. 1. Contact dermatitis: patients with contact dermatitis may have erythema, papules, pimples and other manifestations, and in severe cases, blisters, blisters and other symptoms may occur. 2. Urticaria: patients with urticaria will appear the phenomenon of hives, manifested as round, oval or irregularly shaped pale or red edematous pimples, and some patients will also appear the phenomenon of hives fusion into a piece. The masses disappear quickly and leave no traces. 3. Eczema: eczema patients in the erythema on the basis of there may be a needle tip size pimples, some patients may also appear corn grain size pimples, papules and other symptoms. When patients have allergic acne, it is recommended to be admitted to the hospital for examination and standardized treatment according to the cause.