Children are famous for asking about bodily quirks, but moms don't always have answers. For instance, do you know why boys have nipples? George Holcomb, M.D., surgeon-in-chief at Children's Mercy Hospitals & Clinics, in Kansas City, Missouri, says that in the womb, both boys and girls have breast tissue and nipples. Later, in response to estrogen, teenage girls develop breasts -- so they can eventually breastfeed. Boys don't get that same estrogen surge, so their nipples stay flat. Explain that in terms your kid can understand when he asks. Read on for answers to other head-scratchers.
What to tell your kid: The belly button (or navel) is actually a scar on the abdomen, created when a newborn's umbilical cord is detached from his mommy. Most people have innies -- and whether or not a person develops one is determined in the womb, explains Brad Warner, M.D., Ph.D., a pediatric surgeon at St. Louis Children?s Hospital. In the early months of pregnancy, when a baby is very small, its intestines must develop outside of its body. As the baby grows larger, the intestines coil up and move back inside through a hole where the belly button will later be. The muscle walls under the belly button then grow together to close the gap; if they seal tight, the baby gets an innie. Sometimes, notes Dr. Warner, the muscle walls don't quite close all the way, and the baby ends up with an outie.
Wow! Who knew? About one out of every ten people has an outie, and they occur more commonly among premature and African-American babies.
What to tell your kid: Birthmarks are blemishes that develop on the skin before a baby is born or shortly afterward, says Parents advisor Lawrence F. Eichenfield, M.D., a pediatric dermatologist at Rady Children's Hospital and Health Center, in San Diego. Red birthmarks are made up of extra blood vessels close to the skin's surface. The most common kind, telangiectatic nevi (or stork bites), are pinkish in color and flat, while infantile hemangiomas (also known as strawberry marks) are soft, raised, and bright red. Still other birthmarks are caused by extra pigment in the skin; a few of the most common types include moles, caf? au lait spots -- patches of skin that are light brown and flat -- and congenital dermal melanocytosis (bluish marks known as Mongolian spots, which are most common in babies with darker skin).
Wow! Who knew? Stork bites typically disappear within six to 12 months, while strawberry marks and Mongolian spots usually take several years to go away. Moles and caf? au lait spots do not fade with age.
What to tell your kid: It's likely a holdover from our early ancestors, who needed hair for survival, says William Leonard, Ph.D., professor of anthropology at Northwestern University, in Evanston, Illinois. A hairy body may have looked scary to predators and attractive to females -- and it probably helped our ancestors stay warm.
Wow! Who knew? People whose families come from northern areas tend to have more body hair than those whose families come from warm places. The hair helped in cold climates.
What to tell your kid: Baby teeth begin to loosen and fall out around the time most kids start elementary school -- age 6 or 7 -- in order to make space inside the mouth for our larger, permanent teeth to grow in, says Parents advisor Burton Edelstein, D.D.S, M.P.H, professor at Columbia University College of Dental Medicine, in New York City. Still, our baby teeth serve an important purpose during childhood: They not only allow us to chew the food we need to stay healthy, they're essential for developing speech -- as well as for helping to shape our jaw and facial bones as they grow and develop.
Wow! Who knew? Baby teeth usually fall out in about the same order that they initially erupted: the two bottom-front and top-front teeth first, then the lateral incisors, followed by the molars and canines, with the upper canines last to come in.
What to tell your kid: Ideally, an eyeball's shape should be perfectly round, like a marble, but not everyone's eyes turn out that way. According to pediatric ophthalmologist Dean Fiergang, M.D., of Baltimore, when the shape of the eye is too short from front to back, a person ends up farsighted (meaning it's easy to see things far away, but everything appears blurry close up). On the other hand, if the eye is too long from front to back, a person will be nearsighted (able to see just fine close up but unable to focus on stuff that's far away). Glasses and contact lenses bend and focus light rays so that people with these vision problems can see clearly all of the time.
Wow! Who Knew? As we get older, the lenses of our eyes become harder, which makes it more difficult to focus -- that's why so many more adults wear glasses than kids do.
What to tell your kid: A person's skin color is determined by the amount and type of pigment (called melanin) in the skin, says Dr. Eichenfield. Darker skin, which contains more melanin, helps in sunny places because it's less likely to burn and become cancerous -- so people whose ancestors come from warmer regions, like Africa or Southeast Asia, tend to have darker coloring.
Wow! Who knew? It's harder for dark skin to produce bone-strengthening vitamin D in response to the sun, so people with a dark complexion are especially likely to need a supplement.
What to tell your kid: Over the past 100,000 years, humans' jaws have been growing smaller because, unlike our prehistoric ancestors, we eat mostly soft, cooked foods that require less force (and a smaller mouth) to chew, says Dr. Leonard. But we continue to develop the same number of grown-up teeth (32 in all) -- and squishing 'em all into a reduced-size mouth means they often come in crooked. To straighten their smile and help prevent future health problems, many people wear braces.
Wow! Who knew? People used to wait until all their permanent teeth had grown in (around age 12 or 13) to get braces, but newer research suggests that earlier treatment may actually be more effective.
What to tell your kid: As gross as it might look, snot is produced by special cells in our nose to help keep us healthy. This sticky substance (along with the tiny hairs in our nostrils), traps dust, allergens, and even germs, preventing them from being inhaled into our lungs, explains Dr. Holcomb. The secretions also keep our nose lubricated so the skin doesn't get too dry or become irritated as we breathe in and out.
Wow! Who knew? When we get sick, our body goes into overdrive, producing extra mucus to help flush away bad bacteria, which is why we get a runny nose when we have a bad cold or the flu.
Originally published in the November 2010 issue of Parents magazine.
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