Dirt in the pores does not directly cause blackheads. Blackheads are a type of acne lesion formally referred to as “open comedones”. The sebaceous glands in the skin produce sebum (oil) and can do so in excess, particularly in teenagers and with changes in hormone levels. Comedones form when the pores, which are hair follicles in the skin, become blocked with excess sebum and dead skin cells.
Bacteria can also enter the blocked pore, leading to redness and swelling. With open comedones, the material that clogs the pores (dead skin cells, sebum, and bacteria) is exposed to air, which causes it to turn brown or black (similar to how an apple turns brown when cut), forming what is commonly referred to as a “blackhead”.
Thus, blackheads do not have their characteristic black appearance due to dirt in the pores, but as a result of the contents of the plugged pore turning dark in colour.
Other factors such as heavy or greasy cosmetics, creams, and lotions, perspiration, and oils (from cooking, for example) can contribute to clogging of the pores and the formation of open and closed comedones (which are whiteheads). Washing the face twice daily with a mild, soapless cleanser can help remove the excess sebum which contributes to the development of blackheads.