Acne is an inflammatory condition involving hair follicles. Hair follicles become plugged with keratin and oil produced by the sebaceous glands, which is acted upon by the acne-causing bacteria, creating compounds that are irritating to the skin. Those compounds cause irritation in the hair follicle, resulting in a massive inflammatory reaction. This causes a typical, red acne bump. People with dark skin or those with the ability to tan frequently get brown spots at the site of acne marks. This happens because the surface layer that contains melanin pigment to protect us from the sun is temporarily damaged. This pigment, which is supposed to reside in the top layer of skin (the epidermis), then falls into the deeper layer of skin (the dermis). This is especially true if the person with the pigment is constantly in the sun.