What is there to say about lips? They're essential equipment for eating and speaking, of course. And whistling. And kissing. And we'd look pretty silly without them, wouldn't we?

But if you think that's all there is to say--and know--about human lips, you're in for a big surprise. Just take a look at our list of 13 fascinating facts about lips:

FACT: Your lips are unique.

Many animal species have lips, of course. But only human lips have such a distinct border between the pinkish, reddish parts and the surrounding skin, according to LiveScience. Scientists call this the "vermilion border."

FACT: Your lips can help you choose a mate.

It's hard to kiss without lips, and some scientists believe that kissing plays a key role in mate selection. It seems that locking lips brings potential mates close enough that they exchange biological information--via sniffing another's pheromones. Women are believed to prefer the scent of men whose immune systems differ from their own--and pheromones may be a key to this determination.

FACT: That fleshy bump in the middle of your upper lip has a name.

In fact, that fleshy bump has a few names, including procheilion, labial tubercle, or tuberculum labii superioris.

FACT: Your lips can say something about your sexuality.

Hard to believe, but recent research links the shape of a woman's lips with her ability to achieve orgasm. Specifically, a Scottish psychologist named Stuart Brody found that women with a prominent tubercle of the upper lip are better able to achieve vaginal orgasm. Who knew?

FACT: Bigger is generally better.

When it comes to attracting the opposite sex, big lips are better, the BBC reported. That is, at least where a woman's lips are concerned. But women seem to prefer men with medium-sized lips, a University of Louisville psychologist told the BBC in 2003.

FACT: Your lips aren't the world's biggest.

Unless you're Kristina Rei, that is. The young Russian woman is said to have the world's biggest lips, and no wonder. She underwent multiple silicone injections, all part of an effort to make her lips like those of Jessica Rabbit of the hit 1988 movie Who Framed Roger Rabbit? Did she succeed? See for yourself.

FACT: Lips haven't always been used for kissing.

"Kissing was very restricted up until very recently to areas of Asia--Southeast Asia mainly--and Europe until the conquests in the 1500s," Dr. Vaughn Bryant, professor of anthropology at Texas A&M University, said in a written statement. "No one in the New World kissed, no one in Oceania kissed, the Eskimos didn't kiss, people in sub-Saharan Africa didn't kiss." According to Bryant, kissing started in India and spread slowly after soldiers under the command of Alexander the Great brought the custom home with them.

FACT: It takes many muscles to pucker up.

To pucker up for a kiss - or to play that trumpet - you have to contract your orbicularis oris. Scientists used to think the orbicularis oris was a single sphincter muscle inside the lips. But now we know it's actually a complex of four muscles.

FACT: Red lips can make you rich.

Some have said that lipstick makes women more attractive to men because it makes the lips look more like the vagina's labia. Hmm. But one thing that seems clear is that wearing red lipstick can pay off for women. In a recent study from France, sociologists showed that waitresses who wear red lipstick earn bigger tips--though only from male customers. Waitresses' red lipstick had no effect on the generosity of female customers.

FACT: Lips can become paralyzed.

People suffering from a form of facial paralysis known as Bell's palsy can have trouble smiling or frowning. The condition is caused by damage to the facial nerves. Fortunately, people with Bell's palsy generally recover with time.

FACT: Lips don't sweat.

No wonder--lips simply don't have sweat glands. Since sweat glands also help keep the skin moisturized, that means lips tend to dry out faster than other parts of the body.

FACT: Blood gives your lips their reddish hue.

The skin of the lips is thinner than skin elsewhere on the body, consisting of three to five cellular layers instead of up to 16. Thinner skin means it's easier to see the blood vessels underneath. Of course, this effect is more pronounced in people with light-colored skin.

FACT: Lips get thinner as you age.

Lips get their shape in part from collagen. But as the body ages, the body produces less of this critical protein, and the lips start to lose their plumpness, dermatologist Dr. D'Anne Kleinsmith told Real Simple. Another factor, she said, is ultraviolet light from sunlight. "One way to help preserve the fullness of your lips is to protect them from the sun by wearing a lipstick or lip balm with sunscreen," Dr. Kleinsmith told the magazine.

Also on HuffPost:

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  • We're the only primates with "permanent" ones.

    "No other primate has a permanent breast," writer Carole Jahme (who holds a master's degree in evolutionary psychology) explains in <a href="http://www.theguardian.com/science/2010/may/14/breast-size-evolution" target="_blank"><em>The Guardian</em></a>. "In non-human primates (and other mammal species) a full breast is a clear indication the female is suckling young," she adds. "Not so in humans." Exactly why humans stand alone among the primates, breast-wise, remains unknown. <a href="http://link.springer.com/content/pdf/10.1007/s12110-998-1005-2.pdf" target="_blank">One hypothesis holds</a> that the "perennially enlarged breasts of human females" exist because their size and shape serve as a signal of "residual reproductive value." As <a href="http://www.livescience.com/32745-why-do-women-have-breasts.html" target="_blank">Livescience reports</a>, a more controversial theory suggests that women's breasts became round after the female ancestors of humans stood upright, which also resulted in the "gradual tilting of the pelvis, so the vagina was more oriented to the front of the body." Whatever the reason, the fact remains: humans are the only primates whose breasts remain full permanently, not just around childbirth.

  • The largest natural breasts are a 102ZZZ.

    <a href="http://www.guinnessworldrecords.com/world-records/size/largest-natural-breasts" target="_blank">The Guinness World Record</a> holder for the largest natural breasts is Annie Hawkins-Turner. Her chest measures 70 inches over the nipples and around her back. <a href="http://www.huffingtonpost.com/2011/06/24/norma-stitz-worlds-biggest-boobs_n_884081.html" target="_blank">As HuffPost Style explains</a>, that amounts to 3.5 feet of cleavage (with each side weighing in at 56 pounds), and a bra size of 102ZZZ.

  • Breast orgasms exist.

    Women orgasming through nipple stimulation is an actual thing, and there's science to back it. <a href="http://www.menshealth.com/sex-women/nipple-orgasm" target="_blank">As <em>Men's Health</em> reports,</a> in one study of 213 women, 29 percent said they had experienced a "breast orgasm" at one point or another. A 2011 study in the <a href="http://www.ncbi.nlm.nih.gov/pubmed/21797981" target="_blank"><em>Journal of Sexual Medicine</em></a> that used MRIs to track cortical responses to different types of physical stimulation found that nipple self-stimulation led to activation in the brain's genital sensory cortex, a result the researchers called "unexpected."

  • They make the perfect food.

    When describing the benefits of breast milk and colostrum (the sticky, yellowish substance produced at the end of pregnancy and the first days of a baby's life) the <a href="http://www.who.int/topics/breastfeeding/en/" target="_blank">World Health Organization</a> doesn't mince words, calling it the "perfect food" for babies. Why the glowing recommendation? Breast milk contains antibodies that help babies fight infections and diseases and is easy for them to digest. Its made by cells in the breast called "alveoli," which produce milk in response to the hormone prolactin. It's released when babies suckle.

  • When it comes to milk, size doesn't matter.

    For breastfeeding purposes, it simply doesn't matter whether a woman is an A cup or a D. As board certified lactation consultant (and retired La Leche League leader) Debbi Donovan <a href="http://www.ivillage.com/breastfeeding-there-correlation-between-breast-size-and-milk-production/6-n-137017" target="_blank">explains in an iVillage post:</a> "Larger breasts have a higher proportion of fatty tissue, compared to glandular tissue, but this has no effect on the amount of milk you're able to produce." Though women with smaller breasts sometimes worry they'll be unable to nurse their babies, it's actually women with larger breasts who sometimes have greater difficulties, because of positioning issues, <a href="http://www.ivillage.com/breastfeeding-there-correlation-between-breast-size-and-milk-production/6-n-137017" target="_blank"> she says.</a>

  • They fluctuate month-to-month (and even minute-to-minute).

    Unhappy with your breast size? Give it a minute. That may be overstating things, but not by much. Many women experience breast growth -- as much as a full cup size -- during PMS, because the body has higher levels of the hormones progesterone and prolactin during that premenstrual phase, which can cause swelling, <a href="http://thechart.blogs.cnn.com/2011/08/05/what-the-yuck-can-pms-change-your-boob-size/" target="_blank">CNN reports.</a> Breast growth is also one of the hallmarks of pregnancy, and some sex experts, including the authors of <a href="http://www.salliefoley.com/" target="_blank">"Sex Matters for Women"</a> claim that breasts can swell by up to 25 percent during moments of intense sexual arousal.

  • The left tends to be larger.

    As Jenna Pincott, author of <em>Do Gentlemen Really Prefer Blondes: Bodies, Behavior, and Brains -- The Science Behind Love, Sex, and Attraction</em>, mentions in her book and <a href="http://jenapincott.com/why-is-your-left-breast-larger-than-the-right/" target="_blank">explains in-depth in a blog post on her website</a>, it's perfectly normal for women to have one breast that's larger than the other. And for around 65 percent of women, it's the left one. No one knows why the left side tends to be bigger, although theories abound: One suggests that immune hypersensitivity, which is higher on the left side of the body, has an impact on hormones that help determine breast size and shape; another that women tend to prefer to nurse on their left side (leaving their right hand free) which results in that side producing more milk, Pincott explains.

  • There are four nipple types.

    If you thought there was only one type of nipple, you thought wrong. <a href="http://jezebel.com/5885739/what-type-of-nipple-are-you" target="_blank">As Jezebel writer Tracie Egan Morrissey discovered</a> when she went to visit her midwife for a prenatal visit, there are several common variations: "Normal" nipples stick out a few millimeters from the areola, and then even further when they're aroused or cold; "flat" nipples only protrude when they're stimulated or when temperatures change; "puffy" nipples have a raised areola; and "inverted" nipples (which come in grades) are essentially turned inward. As the <a href="http://www.mayoclinic.com/health/medical/IM02408" target="_blank">Mayo Clinic explains</a>, the latter type isn't necessarily problematic as long as it's always been that way, but if the nipple has only recently turned inward it <em>should</em> be checked by a doctor.