I once had a friend who was a big-time cigarette smoker — so much so that she'd cycle through at least a pack-and-a-half of Marlboros on any given weekend. She'd quit over and over again; inevitably, a few weeks (or more like days) in, I'd find her outside whatever bar we were imbibing at puffing away. Then, one day at brunch, she ceremoniously declared she'd finally be quitting for good. Her reason? "I had my first cigarette in over a month last night, and I woke up with a huge zit on my chin," she alleged.I raised an eyebrow. Not because I expected her to fall off the wagon as quickly as she had in the past, but because I was super-skeptical of her reasoning. "I don't think a zit would show up on your face that quickly after a single cigarette," I argued. "There's, like, bodily functions that need to go down first." But she persisted. The cigarette she smoked 12 hours ago had caused the breakout. I was the one who was wrong.Eventually, she did quit for a while, and then started smoking again, and our friendship eventually fizzled the way these things do. But our argument continued to nag me: Could things really go south so quickly on your face?So I polled dermatologist Jessica Weiser, MD , about how quickly certain stressors impact your skin — everything from smoking to sugar to fast food. Read on to learn how bad habits really affect your face.The grown-up guide to dealing with acne. Read more from The Acne Diaries here