Red forehead and pimples may be eczema, inflammatory acne, polymorphic solar lentigines and so on. 1. Acute eczema: lesions are often manifested as erythema on the basis of the needle tip to the size of a grain of pimples, can also be fused into a piece, the border is not clear, is a variety of causes of inflammation of the superficial dermis and epidermis, easy to recurring episodes. 2. Inflammatory acne: It occurs in areas with dense sebaceous glands, such as the cheeks and forehead, and is often accompanied by exuberant sebum secretion. It is highly prevalent in adolescent men and women, and is related to the abnormal level of androgens and the increase in sebaceous gland secretion. 3. polymorphic sun rash: this is an idiopathic photosensitive skin disease, the onset of most of the season in the spring and summer, the onset of the site is the exposure area. For example, wearing a mask can cover the sides of the cheeks and the nose, but not the forehead, which will appear pimples, papules, erythema, etc. after several days of sun exposure. There are many other conditions that can cause redness and pimples on the forehead, and they should be seen as soon as possible for a differential diagnosis and regular treatment.