Dark spots on forehead are considered to be related to ultraviolet radiation, chloasma, melanosis, melanocytic nevus and so on. 1. Ultraviolet radiation: If patients do not pay attention to head care in daily life, prompting the forehead area to be irradiated by ultraviolet rays for a long time, it may lead to solar dermatitis, which will leave behind the phenomenon of dark-brown pigmentation after healing. 2. Chloasma: the cause of chloasma is still unclear, and it may be related to genetic susceptibility, ultraviolet radiation and changes in sex hormone levels. Patients’ lesions are characterized by light brown to dark brown spots or patches, which may be aggravated by sunlight exposure and persist. 3. Melanosis: The recurrence of the causative factors of melanosis may be related to special medications, chronic constipation, etc. For those with skin melanosis, the typical manifestation is the appearance of grayish-purple grid-like hyperpigmented plaques on the skin lesions, the surface of the plaques is covered with dust-like skin debris, and itching sensation may occur after sunlight exposure. 4. Melanocytic nevus: Melanocytic nevus may be related to gene mutation, trauma, medication and so on. Generally, patients have no conscious symptoms, but local skin may appear spots, papules, plaques, etc., which may be brown or dark brown, so the disease may cause some patients to have dark spots on forehead. It is recommended that people with dark spots on forehead should go to regular hospitals for medical examination in time, and follow the doctor’s instructions for treatment after clarifying the disease.