There are many reasons why two-year-old babies have small bumps on the back of their hands, such as prickly heat, sweaty herpes, ringworm, eczema, contact dermatitis and other causes. 1. prickly heat: high external temperature, skin sweating, sweat discharge is not smooth, may cause the sweat ducts blocked, narrowed, which causes protruding skin pimples, resulting in two-year-old baby hand on the back of the small pimples. 2. Sweat herpes: the etiology is not completely clear, may be related to genetic factors, environmental factors, immune factors, allergic factors, may lead to two-year-old babies have small bumps on the back of the hand, herpes mound, itching and other symptoms. 3. Ringworm: ringworm caused by fungal infection may also lead to small blisters, papules, flaking and itching symptoms on the back of the hands of two-year-old babies. 4. eczema: the skin inflammatory reaction caused by internal and external stimulation of a variety of factors, can also lead to skin erythema, pimples, blisters, itching, may cause two-year-old baby hands on the back of the small bumps. 5. contact dermatitis: the skin on the back of the hand in contact with irritating substances or sensitizing substances leading to skin inflammatory reaction, may also lead to two-year-old baby hand on the back of the small bumps. Two-year-old baby hand on the back of small bumps, there may be other reasons, need to go to the regular hospital in time to check, clear cause.