There are a few common causes for pimples on the forehead.
 Hair gel (clogs your forehead skin pores and causes forehead pimples).  You do not shampoo enough. Oily unwashed hair that is in contact with your forehead skin will make your Acne worse.  You frequently wear helmets, baseball caps or headbands. These will cause friction to your skin resulting in breakouts and more forehead pimples.
Look for a good leave on anti-acne cream. (The benzoyl peroxide area of your plan). The Use a very gentle cleanser and in the morning oil free moisturizer of makeup.
If you do sports or sweat a lot on your forehead you may use stri-dex wipes to wipe up your sweat and unclog your pores in the same time.
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