Blackheads and whiteheads are a combination of skin lipids (oils), sebum and cellular fragments (keratin) that form firm to hard plugs within hair follicles. When bacteria is added to this combination, the condition can lead to acne.
Blackheads are open to the skin’s surface and become darkened at the surface by exposure to oxygen. They are called open comedones (or comedo), Whiteheads are deeper within the follicles and closed from the surface (so they do not turn brown- do not oxidize). They form a light or yellow-white lump and are called milia (or milium).
Comedones and milia are caused by excessive cellular exfoliation within the hair follicle, which can quickly clog or block the follicle.
Some skin specialists believe individuals who are prone to blackheads or whiteheads produce sebum that is drier than normal and conducive to forming firm plugs. It is possible that people with excessively dry skin will have dry sebum , prone to forming plugs. The blockage of bacteria within the follicle may lead to acne vulgaris or cystic acne as infections develops.