字幕表 動画を再生する 英語字幕をプリント Your nails can tell you a surprising amount about your health — whether you have an infection or a serious illness, for example. But not all weird-looking spots on your nails are that big of a deal, including one of the more common issues: white lines or spots. They might seem concerning, especially if you spend too much time on WebMD. But good news: these little lines and spots are benign! Most of the time, anyway. The formal name for the discoloration is punctate leukonychia, also sometimes called milk spots. There are a lot of myths about what causes these white spots: some people say they're a sign of calcium deficiency, or maybe a zinc deficiency — but neither of those things are true. Instead, white lines that go across the nail, parallel to the nail bed, are usually a sign of trauma to the nail. Meaning, you probably hit your nail, or you bumped it against a desk or a table. The trauma may have been slight enough that you hardly noticed it happened, and quickly forgot about it. But the matrix at the base of the nail, which makes new nail cells, got a bump. That bump disturbed the nail-making process, and it shows in the form of a white spot or white line. But nail growth takes a while. Your fingernails only grow about 3.5 millimeters a month, so it takes some time for the line to appear. As the nail grows, the line moves closer to the tip of your finger, until you eventually clip or file it off. And in the meantime, it's nothing to worry about. Probably. White lines that run across your nail might be the ghost of an old bump, but they can also indicate a fungal nail infection, or an infection with a high fever like measles, malaria, or leprosy. When your body is fighting a severe illness, it shifts priorities from stuff like growing nails to the more important task of keeping you alive. So the white lines on your nails show what's essentially a temporary pause. But by the time the lines showed up, you'd already know you'd been sick from all of the other, much more unpleasant symptoms of these diseases. If you have whitish bands running parallel to your nail bed on all your fingernails, you might have what are known as Mee's Lines, a sign that you've been poisoned by lead or arsenic. These lines are actually deposits of lead or arsenic in the nail. They usually appear two months after the poisoning, so again, by the time you'd see them, you'd probably already know you'd been poisoned. So if you see white lines on your nails and nothing else seems to be wrong, you are probably fine. But of course, check with your doctor if you're worried. Thanks for asking, and thanks especially to all of our patrons on Patreon who keep these answers coming. If you'd like to submit questions to be answered, or get some videos a few days early, you can go to patreon.com/scishow. And don't forget to go to youtube.com/scishow and subscribe!