Oil production in the sebaceous glands increases during puberty, causing comedones and acne to be common in teenagers.
Acne is also found pre-menstrually and in women with polycystic ovarian syndrome. Smoking may worsen acne.
Oxidation rather than poor hygiene or dirt causes blackheads to be black. Washing or scrubbing the skin too much could make it worse, by irritating the skin. Touching and picking at comedones might cause irritation and spread infection. It is not clear what effect shaving has on the development of comedones or acne.
Some, but not all, skin products might increase comedones by blocking pores, and greasy hair products (like pomades) can worsen acne. Skin products that claim to not clog pores may be labeled noncomedogenic or non-acnegenic. Make-up and skin products that are oil-free and water-based may be less likely to cause acne. It is not known whether dietary factors or sun exposure make comedones better, worse or have no effect.
A hair that does not emerge normally can also block the pore and cause a bulge or lead to infection (causing inflammation and pus).
Genes may play a role in the chances of developing acne. Comedones may be more common in some ethnic groups. Africans and African-Americans may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation.