6 Surprising Things You Didn't Know About Your Breasts

Boobs. We’ve all got them — but how much do you really know about them? Did you know that the skin on your breasts is especially thin? Or that humans are the only mammals whose breasts stay full even when they’re not nursing? We’ve rounded up six surprising facts that will make you think twice about how you see your twins.

1. Your sleeping position affects your breasts

You may want to think again about how you sleep. CNN published an article on sleeping positions, revealing that if you sleep facing downward or on your side, your breasts may change shape over a long period of time. More specifically, sleeping on your stomach is bad for your breasts because they are pressed against your mattress for hours, and sleeping on your side causes their ligaments to stretch over time The best sleeping positions for your breasts is on your side with a pillow under them for support, or sleeping on your back.

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2. Your boobs get fat

Plastic surgeon and associate professor of surgery at Northwestern's Feinberg School of Medicine Laurie A. Casas explained to Cosmopolitan that as you get older, the glands and collagen in your breasts shrink and are replaced by heavier breast tissue that will be more susceptible to gravity and start sagging. This process can be slowed down, but not prevented, by wearing an underwire bra.

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3. Smoking affects your breasts

As if you needed another reason not to smoke, researchers found that smoking leads to saggy breasts. According to University of Kentucky plastic surgeon Brian Rinker, "Smoking breaks down a protein in the skin called elastin, which gives youthful skin its elastic appearance and supports the breast." Put that cigarette down!

4. Your boobs don’t weigh much

Cosmo reports that "an A-cup clocks in at only a quarter pound; a B, about half a pound; a C, three-quarters of a pound; and a D, around one pound." How they got those measurements, I’ll never understand.

5. Your left is probably larger

There is no such thing as a perfectly symmetrical set by nature; a single pair can vary in breast size, nipple size, and even nipple direction. Scientists aren’t sure why, but size variations in breasts normally occur because there is more tissue in the left breast. In fact, the Huffington Post found that this applies to 65 percent of women.

6. Yours might still be growing

Surprisingly, Planned Parenthood Toronto states that breasts can grow past puberty and into your early 20s. After your 20s, though, the only ways to get more busty are pregnancy, plastic surgery, and certain birth control pills.

So remember to take care of your boobs… you only get one set!