Darkening on both sides of the face can be caused by sun exposure, exposure to coloring agents, post-inflammatory hyperpigmentation, and melanosis. 1. Sunlight exposure: prolonged sunlight exposure can cause localized pigmentation, resulting in the appearance of blackness. 2. Exposure to coloring agents: Exposure to black coloring agents and other chemicals on both sides of the face can cause them to turn black. 3. Post-inflammatory hyperpigmentation: Neurodermatitis, chronic eczema and other inflammatory skin diseases occurring on the face can cause an increase in localized melanin after the disease has healed, resulting in the appearance of blackness on both sides of the face. 4. Melanosis: mostly associated with malnutrition, vitamin deficiency, friction, endocrine disorders, etc., can be manifested as black cheeks on both sides. There may be other causes of blackness on both sides of the face, should be timely medical treatment, standardized treatment under the guidance of specialists, will help to alleviate the uncomfortable symptoms as soon as possible.