Your nails are made from a protein known as keratin, unlike bones, which are made mostly of collagen. Keratin protects nails from damage by making them strong and resilient.

Keratin forms the cells of your hair and skin, too. It also forms cells that are a key part of many glands and that line internal organs.

Read on to learn 17 things you might not know about your nails.

Nails start growing under your skin. As new cells grow, they push old ones through your skin. The part you can see consists of dead cells. That’s why it doesn’t hurt to cut your nails.

Tiny blood vessels, called capillaries, sit under the nail bed. Blood flowing through the capillaries helps nails grow and gives them their pinkish color.

The nails you can see are dead and have no feeling. However, a layer of skin under the nails, called the dermis, has sensory nerve endings. These send a signal to your brain when pressure is applied to your nails.

And toenails grow about 1.5 millimeters per month. Those are the averages for healthy adults. Whether you’re getting proper nutrition and how well you take care of your nails can affect the growth rate.

Although the myth about nails growing after death isn’t true, there’s a reason it exists. After someone dies, their skin dehydrates and shrinks, making it look like their nails grew.

Their hair grows faster than women’s, too. The one exception is during pregnancy, when a woman’s nails and hair might grow faster than a man’s.

If you’re right-handed, you might’ve noticed the nails on that hand grow faster than on your left and vice versa. This could be because that hand is more active (see item 11).

Nails grow faster in summer than in winter. Not much research has been done about why this happens, but one study involving rats found that cold weather stunted their nail growth.

Using your hands a lot makes your nails more prone to minor trauma from things like tapping them on a table or using a keyboard. This promotes blood circulation in your hands, stimulating nail growth.

About 10 percent of all dermatological conditions are nail-related. Yellow, brown, or green nails usually mean you have a fungal infection. In some cases, yellow nails are a symptom of a thyroid condition, psoriasis, or diabetes.

White spots or lines are usually caused by minor injuries to your nail, like from biting them. These spots are typically harmless and will grow out.

Stress can cause your nails to grow more slowly or even temporarily stop growing. When they start growing again, you might have horizontal lines across your nails. They’re usually harmless and will grow out.

Also called onychophagia, nail biting usually doesn’t cause long-term damage. However, it raises your risk of getting sick by spreading germs to your mouth. Damage to the skin around your nails could cause infection, too.

To keep nails healthy, take breaks from using polish or having artificial nails. Using and removing these products can be hard on your nails, so taking a break from them helps nails repair themselves.

Nail growth and other nail characteristics partly depend on your inherited genes. Other factors include your age and health status.

This small sliver of skin at the base of your nail protects the new nail from germs as it grows through your skin. You shouldn’t cut your cuticles. Doing so removes the important barrier that helps prevent infection.

Primates, including humans, have nails instead of claws as well as opposable thumbs. This gives humans more agile hands that allow us to grasp things better than other mammals.

Your nails give you a picture of your overall health. Changes in your nail color or a disruption in their growth could be symptoms of a medical condition, poor nutrition, or excessive stress. Talk to your doctor if you’re worried about recent changes to your nails.

Follow these tips for good nail hygiene:

  • Trim your nails regularly, keeping them short.
  • If you do have longer nails, scrub the underside
    of them when you wash your hands. Use soap and water every time and consider
    using a nail brush as well.
  • Sanitize nail grooming tools before each use
    (and make sure any salon you visit does the same).
  • Don’t bite or chew
    your nails.
  • Avoid ripping or biting off hangnails.
    Instead, use a sanitized nail trimmer to remove them.