A hard lump on the chin on the left side of the face can be caused by keloid, boils, sebaceous cysts, and so on. 1. Keloid: If you often squeeze the pimples on your chin when you have pimples, it is easy to form keloid after the healing process, which will cause a hard lump on the left side of your chin. 2. Boils: If purulent inflammation occurs in the deep part of the hair follicles and the surrounding tissues on the left side of the chin, boils can be formed, which can also lead to a hard lump on the left side of the chin, usually accompanied by local redness, swelling, heat and pain, pus oozing and other symptoms. 3. Sebaceous cysts: the sebum secreted by sebaceous glands cannot be discharged normally, and accumulates in the glands, which can form cysts, which can lead to hard lumps on the left side of the chin, and usually do not have other symptoms, but can be accompanied by pain if it presses on the surrounding tissues; if it is secondary to an infection, it can be accompanied by redness, swelling and pus, and other symptoms. There are many other causes of a hard lump on the left side of the chin, which should be taken seriously, and the cause of the problem should be identified in time, and further treatment or therapy should be prescribed by the doctor.