Andrew Huberman· PhD
Now you hear different things like if you pinch the skin on the top of your hand and it takes more than three seconds to lay down again flat, then you're dehydrated. You hear that, you hear, okay, if you are to press on your fingernail and see a change in the color of the tissue, just be below your fingernail, which indeed does happen, and it does not go back to its original color within one to three seconds, then you're dehydrated. You hear things like this if your ankles are swollen when you're wearing socks, you take off the socks and you can see the imprint of the socks on your lower limbs, that means you're dehydrated. You hear this kind of stuff, and you should probably be wondering, is any of that true? To some extent, it is true, although it can vary quite a bit by how old you are, whether or not the skin on the top of your hand tends to be looser or not depending on whether or not you're leaner or not. So in other words, those are not absolutely objective measures of dehydration.