Fingernails and toenails, they’re not just for decoration. They protect your fingers and toes and help you pick up tiny things, like splinters or that piece of spinach stuck between your teeth after lunch. And they can also tell you a lot about your health. Nails are collections of dead cells that grow from a root called a Matrix hidden just beneath your cuticle, the lighter crescent shaped area at the base. The matrix constantly makes new cells called Plate Cells, and each layer pushes the old, dead plate cells out of the cuticle. When nails start to grow differently or even change color, it usually means that there is something wrong with the matrix or with the surrounding tissue. So by working backward, you can often figure out what’s doing the interfering, and in the process maybe learn something about what’s going on in your own body. Beau’s Lines, for example, are horizontal ripples on the surface of the nail. They look like little waves, and they form when the matrix stops producing new cells for a while. When the matrix starts making new cells again, they push the nail out as usual, but there is an indentation marking the spot where it stopped, kind of like a tree ring. And there’s a reason why the matrix would’ve hit the pause button. Probably, it wasn’t getting enough nutrients from the blood stream. Usually, that means the person has an infection or some other kind of serious illness. That’s why people who have high fevers for a while, often develop Beau’s lines a month or two after- -wards. Pitted nails are another potential matrix issue, where the nails surfaces have indentations that look like very small pot holes. The pits are linked to skin disorders, like Psoriasis and Eczema, which can cause inflammation of the matrix. An inflamed matrix produced new plate cells unevenly, so you end up with depressions on the nail surface. Nails can also change color, something you’ve probably noticed if you’ve studied your nails on a cold day, and realized they were blue. Generally, that means that your extremities aren’t receiving enough oxygen. Blood with low oxygen is darker and reflects light differently through your skin making your nails look blueish. It could just be your body reacting to cold by constricting your blood vessels, but a person whose blood isn’t receiving enough oxygen could have a respiratory illness, like asthma or emphysema. Blue nails can also be a sign of Raynaud’s Disease. A disorder marked by spasms in a person’s blood vessels that narrow them. The narrowing reduces blood flow to the extremities, so they get blue nails. Now blue nails, it not actually the nail changing color, it’s the bed underneath it. But nails can also turn yellow, and that’s actually the nail changing color, this can happen for a lot of different reasons. In most cases, it’s cause by a fungal infection known as Onychomycosis. Yeast or mold sets up shop within the actual nail plate, turning it yellow. It doesn’t smell to good either. Other times, the yellow nails means something more serious, like Yellow Nail Syndrome, which doesn’t sound super serious, but it happens when the matrix does produce new plate cells but very slowly, so they pile up and create a thicker yellow-ish nail plate. But like Beau’s Lines, Yellow Nail Syndrome is caused by something else. It could be a chronic respiratory disease, which would reduce the nail’s oxygen supply and slow growth. Or it could be sign of an issue with the Lymphatic system, which distributes protein rich fluid throughout the body. Usually, that issue is cancer or aids. A black or brown streak in a nail can also be super serious, or nothing at all. In some people that streak can signal Subungual Melanoma, a form of skin cancer that affects the nail bed, which is the skin underneath the nail plate. Melanoma often changes the color of the skin, including the skin under nails. But the streak also might be harmless, if you have a darker complexion it’s completely normal. So it could be something, or it could be nothing. Which is why of you’re worried about the color or the look of your nails, here’s a tip. Don’t get all your medical advice from the internet! These changes can mean more than one thing, so talk to a real doctor before jumping to any conclusions. We are not a real doctor. Thanks for watching this episode of SciShow, which was brought to you by our patrons on Patreon, who give us money so that we can do this, which is really nice. If you want to help support this show, you can go to Patreon.com/SciShow and do not forget, if you want to get smarter with us, to go to YouTube.com/SciShow and subscribe.