Acne on forehead in 40s can be categorized into physiological and pathological, and pathological causes include skin diseases and endocrine diseases. 1. Physiological: If you have recently eaten spicy, cold stimulating food, or greasy, too much sugar content of food, such as milk tea and hot pot, etc., there may be the case of forehead acne, which is a normal physiological phenomenon, because eating these foods will lead to sebaceous glands secretion of the pores and thus clogging, maintain a healthy diet can be restored, without additional special treatment. 2. Pathological: If you suffer from skin diseases, such as folliculitis and seborrheic dermatitis and other diseases, it will be manifested as pimples on forehead because of clogged pores; there are also endocrine disorders that can lead to this symptom because of the strong secretion of sebaceous glands of the skin, such as endocrine disorders and so on. If you suspect that this symptom is caused by a pathological cause of forehead acne, it is recommended to go to the hospital in time to consult a doctor to clarify the cause of the disease and then treat the symptoms.