The back of the hand with small bumps and does not hurt, it may be flat warts, seborrheic keratosis, friction moss-like rash or infectious mollusc and other diseases. 1. flat warts: the disease is caused by human papillomavirus infection, through skin contact infection, occurring in the face, neck back of the hand and upper arm. It is a very good idea to have a few of these in the form of scattered flat papules on the skin, and the papules are mostly light brown or flesh-colored. 2. Seborrheic keratosis: this disease may be related to skin aging, is a benign skin growth. It is a benign skin growth that occurs in exposed areas such as the face and the outer side of the upper limbs. It is characterized by scattered light brown or dark brown flat papules or plaques, which gradually increase with age. 3. Frictional mossy rash: It is most common in preschool children and may be related to skin contact with sand or other dirt. The manifestation of the back of the hands and arms on the outside of a dense pinpoint to corn size pimples, pimples without obvious discomfort, can also be accompanied by mild itching. 4. Molluscum contagiosum: The disease is caused by the molluscum contagiosum virus infection, which is prevalent in children, mostly in kindergartens, schools and other places of aggregation episodes. Most in the trunk, armpits and other parts of the hemispherical papules, its surface has a waxy luster, the middle of the navel-shaped depression. It is recommended that patients with painless and itchy bumps on the back of the hands go to a regular hospital in time to get a clear diagnosis and standardized treatment under the guidance of a doctor.