There is a three-centimeter hard lump under the boil, which can be considered as inflammation of the deep part of the hair follicle, carbuncle and so on. 1. Boil: a purulent inflammation that occurs in the deep part of the hair follicle and the surrounding tissues. At the beginning, a follicular inflammatory papule appears on the skin, with basal infiltration, but with the expansion of inflammation to the periphery, it can form a hemispherical firm nodule, with localized redness, swelling, heat and pain manifestations. 2. Carbuncle: If several boils are aggregated, carbuncle can be formed, initially it is an inflammatory lump with redness, swelling and heat pain, later, the lump can gradually increase in size, thus pus breaks out, and there is severe pain and tenderness on the skin. When a lump is formed under the boil, it is recommended to consult a doctor in time for examination and targeted treatment.