Dehydration occurs when your body is losing more fluid than it’s taking in, according to Robert Segal, M.D., founder and medical director of LabFinder. That can happen with exercise, illness that causes diarrhea or vomiting, and loss of body heat.
And it can lead to some pretty serious problems: Driving when you’re just one percent dehydrated, for instance, can lead to pretty dangerous behaviors behind the wheel, like lane drifting or late braking, according to a 2015 study. Plus, if you’re two percent or more dehydrated, your athletic performance might take a hit, too, as we reported.
When the weather is toasty, it’s easy to remember to grab some water, but as it turns cooler, the chances of dehydration can increase, Dr. Segal notes. For example, if you’re running in chilly temps and you’re wearing multiple layers, it can be tougher to keep hydration in mind (Here’s everything you need for cold weather running).
But you should: When you don’t supply your body with enough fluids, you reduce functioning in every system, including our cells, tissues, and organs, he says.
There’s no one, set water prescription for every guy—it depends on things like diet and activity level. Still, there are some ways to know you’re not getting enough. Here, 5 signs you might be dehydrated.
When you lose fluid, the nerve signals from your brain to your muscles don’t work as well, says Dr. Segal. So, it’s easier for muscles—especially in the legs, he says—to react by cramping.
Also, when you’re exercising and losing fluids, you’re creating an imbalance of electrolytes like sodium and potassium in your muscles. Not only does that up your odds of cramping, but it also increases your chances of feeling next-day soreness post-workout.
Organs like your liver use water to function, Dr. Segal says. One of those tasks is releasing glycogen, the molecule that stores sugar.
“If the liver can’t get fuel, it cannot release glucose and other energy stores,” he says. “What do we do in return to try to replace them? Eat.”
Sweet foods are especially attractive when this happens, he adds, so cravings for things like desserts or sugary drinks those could be a dehydration sign.
Part of hydration’s job is to regulate blood volume, including blood pressure. When you’re lacking in fluids, your blood pressure tends to lower, and that can lead to dizziness and lightheadedness, according to David Greuner, M.D., head physician at NYC Surgical Associates.
He adds that dehydration also affects your vestibular system, which is responsible for keeping you in balance. So, in addition to your blood pressure drop, you may also feel vertigo and even become nauseated from feeling off balance.
Related: Why You Feel Dizzy When You Stand Up
With nothing coming in, nothing’s going out. If you’re significantly depleted in your fluid stores, a dropping urine frequency will be a big sign, says Albert Ahn, M.D., clinical instructor of internal medicine at NYU Langone Health.
“If you normally pee every three or four hours and now it’s every eight to 10 hours, you’re likely dealing with some degree of dehydration,” he says.
That can be particularly dangerous because it means that your body isn’t getting rid of toxins as quickly as it should—you could even be setting yourself up for problems like kidney stones, a condition in which dehydration often plays a role, adds Dr. Segal.
Hydration helps every part of your digestive system, from keeping your intestines lubricated and supple, to giving your poop enough moisture to pass out easily.
Without enough water, your stools can harden and then become difficult to get out, according to Heather Bartlett, M.D., a family practice physician in Columbus, Ohio.
Most of the time, symptoms like these are mild, says Dr. Segal, and they can be minimized or eliminated by simply drinking more water.
“Listen to what your body is telling you, and don’t ignore these seemingly meaningless symptoms,” he says.
If dehydration is severe, it might be life threatening. So if you’re in a situation where your dizziness is intense, or you have other signs like strong thirst and headache, you may need to seek medical help to get some IV fluids.