There are mainly two reasons behind Pimples. First is your food has too much oil which does not give nutrition to your body. So Don't take fast food. Drink plenty of water.
Second Reason is Behind pimple is that your Face Wash or face cream which does not suit to your skin.
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Pimples may be because of many reasons, one of them being oily skin. The dirt and oil accumulated on the face may be a cause for it. To make your skin less oily, wash your face with water for at least 4 times a day. Use an oil free moisturizer after the face wash. This will not only nourish the skin, but also keep it hydrated properly, removing the excess oils from your face.