Clogged pores, called comedones, are caused by a buildup of secretions and dirt within the opening of the pore. The sebaceous gland lies just beneath the surface of the skin and secretes an oil called sebum through the pores. Sebum combines with dead skin cells within the hair follicle and passes through the pores to exit the body. When this process occurs correctly, the skin remains moisturized and healthy.
Clogged pores begin to form as sebum and dirt accumulate within their openings. There are two forms of comedones: a blackhead and a whitehead. A whitehead, or closed comedo, develops when the pore no longer has an opening and oil continues to accumulate beneath its surface. These comedones can rupture or become infected.
An open comedo has a wide opening on the surface, giving the sebum and dirt accumulation a chance to oxidize from exposure to air. The oxidation causes the melanin within the sebum to turn into a dark brown or black cap, thus the term "blackhead." A blackhead can turn into a pimple. Clogged pores can occur on any skin type, but they are more often found on individuals with oily skin. Whiteheads and blackheads are also forms of acne lesions and can be treated in a variety of ways.