Darkness of the face may be physiologic or pathologic. It is not necessarily a precursor of any disease.
Disease-wise darkness of the face may be some congenital birthmarks such as nevus of Ota, and severe liver disease, hypoadrenalism, nephropathy, diabetes mellitus, hypothyroidism and lipemia may also cause darkness of the face. You should seek medical attention to find out the cause of dark face.
Physiological darkness of the face may be due to congenital dark skin color. If you are exposed to too much ultraviolet light, the exposed area will be hyperpigmented, and you will have a dark complexion, so you should pay attention to sun protection. Irregular diet, nervousness, stress and lack of sleep can also make your face dark. Ageing will also make the skin dark, should pay attention to maintenance. Sitting in front of the computer for a long time, smoking will also darken the face.
Excluding physiological factors should be timely consultation to avoid delayed treatment.