A chin that is suddenly swollen and a little hard can usually be caused by the following reasons:1. There may be inflammation caused by an infection in the soft tissues of the chin. Folliculitis, acne, or inflammation of the soft tissues around the chin, such as inflammation of the gums, may also lead to swelling and hardness in this area.2. It may be caused by swelling of the lymph nodes in the chin. This situation is common in acute upper respiratory tract infection and led to lymph node swelling, in addition to the local hardness, but also feel the chin there are granular things, and when pressed, there will be pain. In addition, it is accompanied by symptoms of upper respiratory tract infection such as dry throat, sore throat, cough, phlegm, nasal congestion and runny nose.