Hard lumps under the skin of thighs may be caused by subcutaneous lipoma, dermatofibroma and other reasons. 1. Subcutaneous lipoma: Subcutaneous lipoma may be related to heredity, chronic inflammation, systemic lipid metabolism abnormality and other factors, and can appear in any part of the body with fat, manifested as a single or multiple skin surface located in the subcutaneous confined lumps, usually in a rounded or lobed shape. 2. Dermatofibroma: Dermatofibroma may be related to trauma, insect bites, viral infections and other factors, preferably occurring in the outer limbs, mainly manifested as a round or ovoid solid nodules on the skin surface, with smooth or rough surface and no other self-conscious symptoms. Hard lumps under the skin of the thighs may have other causes, it is recommended to go to the hospital in time to improve the examination and give targeted treatment after clarifying the cause.