A familiar term for what is medically called a closed comedo. A comedo, the primary sign of acne, consists of a dilated (widened) hair follicle filled with keratin squamae (skin debris), bacteria, and sebum (oil). A whitehead is a comedo that has an obstructed opening to the skin. A closed comedo may rupture and cause a low-grade skin inflammatory reaction in the area.
A pale or white-topped pustule on the skin.
Your pores can become blocked for several reasons. One cause of blocked pores is hormonal changes, which are common triggers of acne. Certain life stages can increase the amount of sebum, or oil, your pores produce. The increased oil production causes clogged pores and whiteheads.