How does red knot itch rise on the face to do

Face itching red pimples, first of all to consider two problems: first, consider allergic dermatitis or urticaria, more common in some environmental substances caused, such as pollen, dust mites, caterpillar venom, some plant secretion juice; in addition, such as the decoration of the house formaldehyde, paint, will cause facial skin allergies, showing erythema, red papules, pimples accompanied by obvious itching. Second, in the skin barrier damaged people, it is vulnerable to changes in temperature, or some external substances, or the use of products will induce allergic reactions, manifested as erythema, telangiectasia, red papules, some small lumps.