The sudden appearance of a bruise on the chin area may be due to the rupture of capillaries under the skin and the accumulation of blood inside the capillaries under the skin. This condition may be caused by some chronic irritation, such as pressing the chin area with the hand. Chronic irritation of the skin is usually not painful or itchy, allowing subcutaneous petechiae to form unknowingly. In addition to this, the clotting time abnormality caused by thrombocytopenia can also lead to petechiae. A coagulation analysis and blood count should be done at a local hospital, and the diagnosis can be clarified based on the results. If it is determined to be a thrombocytopenic disease, it is recommended that the best option is to go to the hematology department for targeted treatment. In addition to certain insect bites or allergic diseases, temporary bruising can also occur.