There is a hard lump on the body may be mosquito bite dermatitis, lipoma, epidermoid cyst and other diseases. 1. Mosquito bite dermatitis: mosquito bite dermatitis usually occurs in the summer, when the living environment is not hygienic, easy to mosquito bites. The toxins released by mosquito bites will cause the body to develop an immune response, such as the formation of hard bumps on the skin, mostly accompanied by pain, itching and other symptoms. 2. Lipoma: Lipoma can occur in any part of the body, is a relatively common soft tissue benign tumor, composed of mature fat cells. Lipoma is mainly manifested as hard lumps formed on the skin surface, which can be pushed by fingers, and accompanied by symptoms such as local pain and numbness. 3. Epidermoid cysts: most of the epidermoid cysts are caused by trauma that leads epidermal cells to enter into the subcutaneous growth, and most of them occur in the face or the upper part of the trunk. Epidermoid cysts are usually solitary, well demarcated from the surrounding tissues, and well-moved. There are more reasons for a hard lump on the body, it is recommended that patients seek timely medical treatment to further clarify the cause of the disease, under the guidance of the doctor to choose the appropriate treatment program.