The blackening of the cheeks on both sides of the face may be a manifestation of certain physiological phenomena or certain diseases, such as skin melanosis, periosteal keratosis, etc., which should be promptly diagnosed to find out the cause of the disease. 1. Physiological factors: If the facial sunscreen is not in place, often subjected to sunlight, may cause skin pigmentation, resulting in black cheeks on both sides. 2. Melanosis: this disease is a pigment metabolism disorder with skin pigmentation as the main manifestation, which can also lead to black cheeks. 3. Perifollicular keratosis: Perifollicular keratosis, also known as hair moss or hair keratosis, is a chronic follicular keratosis skin disease with a certain genetic predisposition, occurring on the outer side of the upper arm and the thigh extensors, but also in the cheeks and buttocks. If you find that the cheeks on both sides of your face are dark, you should go to the hospital in time, ask the doctor to clarify the cause of the disease, and if necessary, carry out the appropriate treatment.