Small bumps on the inner side of the arm are itchy. Consider the following possibilities: 1. Atopic dermatitis: its onset may be strongly related to genetics, while dry skin of the patient is also a characteristic manifestation. Blood tests may see an elevated blood eosinophil fraction compared to normal, as well as a relatively higher total lgE ratio than normal. 2. Psoriasis vulgaris: in addition to bumps, flaky erythematous patches with silvery-white scales may be seen. The etiology may be related to enhanced dermal vascular inflammation, as well as immune disorders, genetics and other factors. 3, lichen planus: may be related to genetics, immune disorders and other factors.