Pimples are also known as acne, and the possible causes of hardening of pimples include excessive local inflammation, nodular acne, hyperplastic scars, and so on. 1. Excessive local inflammatory response: when acne is still in its early stages, it is mainly manifested as closed pimples. When there are situations such as aggravation of local infections and excessive extrusion, the patient’s local inflammatory response at the site of closed pimples will be aggravated, which will make the local tissues’ tension increase, and manifest as hardened pimples. 2. Nodular acne: If the patient does not squeeze or stimulate the acne, the acne naturally hardens and increases in size, and subcutaneous nodular damage can be felt in the acne area, then this may indicate that the acne condition has progressed, and fibrous tissue hyperplasia has occurred in nodular acne, which belongs to the heavy type of acne, and needs to be treated by the patient in a timely manner. 3. Proliferative scars: If patients often scratch, touch, squeeze, stimulate the acne may make the acne localized erosion, ulceration, which leads to the emergence of scar hyperplasia, so that the skin in the acne area hardened; these scar hyperplasia is usually higher than the normal skin, with different shapes, may be accompanied by redness, swelling and itching, etc., which can be improved by freezing, laser and other treatment methods. To summarize, it is recommended that patients with hardened acne go to the hospital for timely treatment to avoid further aggravation of the condition; and it should be noted that the above treatments should be carried out under the guidance of a physician to avoid the occurrence of adverse reactions.