A lot of pimples in the middle of the forehead are symptoms of acne, folliculitis or papular urticaria, and need to go to the hospital for a clear diagnosis. 1. Acne: Acne is mainly caused by localized keratinization of the follicular opening and the growth of Propionibacterium acnes. It is related to bad habits such as staying up late, love of sweets, love of fried food, and drinking alcohol. 2. Folliculitis: Folliculitis is caused by Staphylococcus aureus infection, usually localized skin with breakage and trauma, caused by bacterial invasion, children or immunocompromised people are prone to have. 3. Pemphigus urticaria: Pemphigus urticaria is also called insect bite dermatitis, most commonly seen in the summer and fall nights, is the bite of mosquito venom caused by a local allergic reaction caused by. Pimples appearing in the middle of the forehead, should go to the hospital in time, clear diagnosis and then treatment.