You go to bed with skin clear as a newborn's and wake up with an angry red zit on your forehead -- but that pimple is no overnight star; it was actually days in the making.
"Sebum naturally migrates out of the follicle to the surface of the skin, but if there's a buildup of dead skin cells or you're using a product that's comedogenic, the process can be interrupted and the pore can eventually become blocked and infected," explains Brentwood, Calif.-based cosmetic dermatologist Dr. Jessica Wu, noting that most zits take about seven days to form.
Of course pores can be come more instantaneously blocked with a product that's not meant for the face, such as misdirected hairspray, warns Dr. Kenneth Beer, a dermatologist in Palm Beach, Fla. Pimples can also appear to pop up overnight pre-period, but this is due to a gradual increase in oil production that's the result of cyclical hormonal fluctuations.
