Flat warts are about the size of a pinhead and usually appear on the face, but can also appear on arms, knees, or hands.Other possibility is
of eczema. It is a form
of chronic dermatitis (rash).Allergic reaction is one of the important causes of eczema. Allergic reaction can occur to strong soaps, certain foods, plants, metals, cosmetics, dust mites etc.
I think that you should get it evaluated from a dermatologist as treatment modalities for all are different.
I hope it helps.