A hard lump on the baby’s hand may be related to common warts, fibroma, tendon cysts and other causes. 1. common warts: after the skin of the hand is infected with human papilloma virus, it can cause abnormal proliferation of skin tissues in the area, and hard bumps can appear. 2. Fibroma: round in shape, usually brown skin growths, relatively hard texture, can be manifested as hard bumps on the hand. 3. Tendon sheath cysts: when suffering from tendon sheath cysts, they can protrude from the surface of the hand and appear as hard bumps. Parents are advised to take their babies to regular hospitals in time to clarify the cause of the disease and standardize the treatment under the guidance of the doctor, so as not to bring adverse effects to the body due to the delayed condition.