A hard bump on the forehead may be caused by sebaceous cysts or boils. 1. Sebaceous cysts: After the sebaceous gland ducts are blocked, the contents of the sebaceous glands gather in the pores to form hard knots protruding from the skin, which may be accompanied by redness, swelling, pain, and milky-white soya bean residue-like objects that flow out when they burst, and are usually treated by small surgical incisions to clear out the contents or complete surgical excision. 2. Boils: Due to localized follicle infection with Staphylococcus aureus, the deep tissues of the follicle become suppurative, manifesting as a red lump, which may have pus spots in the middle, and is usually related to immunocompromise. It can be treated with oral cefuroxime tablets, levofloxacin capsules or topical mupirocin ointment. There may be other reasons why a hard bag on the forehead hurts when pressed, so it is recommended to go to the dermatology department, improve the examination to clarify the cause of the disease, and then carry out regular treatment under the guidance of the doctor.