Comedones: Comedones are commonly referred to as blackheads and whiteheads, and are the least severe types of acne. A comedo forms when residual skin oil, makeup, dirt, dead skin, and small hairs impact a sebaceous follicle and prevent the pore from functioning correctly. The result is a small impaction that is neither red nor painful. If the pore is open, the comedo will be dark in appearance and is thus called a blackhead. If the pore is closed, than the comedo is referred to as a whitehead, and is flesh-colored in appearance.