What an Expert Said Could Happen: The act of your face rubbing against your pillow can push the makeup into your skin and clog your pores, says Neal Schultz, M.D., board-certified dermatologist in New York City and creator of BeautyRx. If you have acne-prone skin (like I do), this can lead to breakouts. Great, I was really in for it.

"When most women sleep with their makeup on, they get away with it," says Schultz. "If you're not acne-prone, then the downside from occasionally doing it is eye irritation." The keyword here: occasionally. "The reason we wash our face is so that we don't have coatings of impurities that don't belong there," says Schultz. "These can only clog and irritate the skin."

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What Actually Happened: The first day of the experiment, I applied a handful of products (liquid foundation, cream highlighter, mascara, sparkly eye shadow and lip gloss) before heading to work. By the time 11 p.m. rolled around, it took all my willpower not to run to the sink and scrub my makeup off before my head hit the pillow. My foundation felt so heavy, and my face started itching. I tossed and turned thinking about what was sitting on my face.

When I woke up (after a not-so-great night of sleep), my skin looked shiny, AND I noticed a couple of small whiteheads starting to form. Some of my mascara had smeared under my eyes, and my gloss had worn off -- not as bad as I expected. Phew.

My eyes, though, were a different story. They were really red. The next day, I switched mascaras, and my eyes didn't feel as irritated the next morning. As the week went on, I got more comfortable with the feel of foundation on my skin, so by the end of the week, I wasn't bothered by it come bedtime.

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What an Expert Said Could Happen: "Not cleansing for a few days is unlikely to do any long-term damage, as long as it does not become a habit," says Shari Marchbein M.D. board-certified dermatologist and clinical assistant professor of dermatology at NYU School of Medicine.

Score one for all my fellow lazy girls. But, Marcbein adds that not washing your face on the reg could lead to dryness, irritation or even contact dermatitis from makeup and dirt. "Most dermatologists agree that we need to wash our face at least once a day," she says. "For those who have very sensitive skin, this may be enough. However, for those who are oily, wear heavy makeup (especially if it is not oil-free) or those who are exercising, it is recommended that you wash morning and evening."

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What Actually Happened: After waking up with a full face of makeup, my skin was as greasy as a slice of pizza. Every one of my pores felt clogged. It was like my face was being suffocated. While I could easily go 72 hours without washing my face when I wasn't wearing any makeup, I just couldn't do it now. I caved and used Lumene Lahde Micellar Cleansing Water to take off my foundation and eye makeup every morning (except for the very last day of this experiment, which I'll get to later). Ah, sweet, sweet relief. My skin could finally breathe -- until I applied my makeup all over again, that is.

What an Expert Said Could Happen: Washing your face before working out is a whole lot more important than doing it afterwards, says Schultz. Think about it: Anything that's gotten onto your skin up until that point (like makeup, dirt, debris, and air pollution, to name a few) can be pushed into your skin if you wipe your face dry with a towel, explains Schultz.

"Most people don't pat their face dry -- they wipe their face dry, pushing that crap into their pores," he says. Now, if you hit up the gym sans makeup and bypass the locker room without rinsing your skin when you're done, it's not the end of the world. Schultz points out that sweat contains urea, which is actually a moisturizing ingredient.

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