Running Dehydration Symptoms To Look Out For


Exercise indeed has a ton of benefits for your body. But you still need to be careful how you do it. While it’s highly beneficial, getting small things wrong can produce undesirable results. Aside from getting your form right, one of the biggest things you must watch for is dehydration.

Here are the most common running dehydration symptoms to look out for. Stay properly hydrated, keep an eye out for these symptoms, and you should notice that your performance improves when you’re taking in the right amount of water.

What is Dehydration?

Dehydration is when you have an inadequate amount of fluid—i.e. water—in your body, which begins to negatively impact multiple processes.

For runners, it’s commonly caused by losing more fluid than you’re taking in—in other words, sweating out more fluid than you’re drinking.

Even a small shift in the fluid balance within the body can lead to several unpleasant consequences.

Why Is It Important to Be Aware of When Running?

Being aware of dehydration while running is essential. By the time you feel thirsty, you’ve already started to dehydrate, so paying attention to your symptoms can make a big difference in preventing dehydration from setting in and causing problems.

As you dehydrate more and more, it begins to negatively affect the body, impacting your performance.

The more water you lose, the thicker the blood becomes. This means the heart has to pump harder to send it around the body, placing a greater strain on your cardiovascular system.

Your body then also prioritizes sending blood to the muscles, so they can continue to support you through the run. However, this means it sends less blood to the skin for heat release, making it easier to become overheated.

In a nutshell, dehydration can lead to discomfort and reduced performance, and heatstroke at its worst. Paying attention to it while running can save your performance and health!

How Do You Know If You’re Dehydrated While Running?

The first step to beating dehydration is learning the symptoms. Paying attention to your body will help you spot the early signs and rehydrate before it becomes a worse problem.

Early Signs of Dehydration

These are the first subtle signs of being dehydrated. If you rehydrate immediately upon noticing these, you should be pretty all right during your run.


When you notice that you’re thirsty, you’re already dehydrated. The key is to take a small sip of your drink every few minutes so you never get to that point.

Dryness of Mouth

Your mouth may get dry the more dehydrated you are. But if you breathe through your mouth when running, the air could dry out your mucus membranes. You should work on nasal breathing, but that’s a topic for another article!

A dry mouth typically means your body has little fluid left to work with. If you notice it, take a few sips immediately.

Flushed Skin

You might not notice this, but if your running buddy asks why you’re suddenly so flushed, dehydration could be to blame.

As you get more dehydrated, your body can start to overheat. In this case, your body has started to redirect the blood to the skin to let excess heat escape, but this comes at the expense of blood to the muscles. Flushed skin may be accompanied by other symptoms for this reason.

Serious Symptoms of Dehydration

These symptoms are an indication of more severe dehydration. By this stage, your body is starting to take the strain due to lowered fluid levels, so we highly advise stopping your exercise and rehydrating before things get more serious.

Increased Body Temperature

This is a step up from the early signs of dehydration. When you’re sweating, flushed, and feeling warmer, it’s a sign that your body is on the road to heat exhaustion. At this point, you need to stop and rehydrate before your health takes a nasty turn.

Increased Fatigue

Once your body starts redirecting blood away from the muscles and to the skin, you’ll notice the fatigue beginning to set in. Without a constant supply of oxygen and nutrients, your muscles need to dig into their glycogen supply to push you forward, but it tends to deplete fairly fast.

Increased Perception of Effort

With increased fatigue comes an increased perception of effort. You may feel like it’s much more difficult to run the next mile than it’s ever been before. If you wear a smartwatch, you might notice that your pace drops and your heart rate increases.

Gastrointestinal (G.I) Distress

With your blood being directed towards the muscles and skin, the stomach is left without its usual supply of blood to aid in digestion. If you’ve had a pre-run meal, even a mid-run energy bar, or chew, your digestive system may start to play up.

Without the usual blood supply, the digestive process is essentially halted as the blood deals with other, more pressing issues. However, this can quickly lead to gastrointestinal distress, most commonly in the form of cramps.


You may also find that your head begins to pound as it’s getting less oxygen, and your heart is beating harder to get the blood up there. At every step, it may feel like your headache is getting worse and worse.

Heavy Breathing and Increased Pulse Rate

With less fluid in your body, the blood becomes thicker and harder to pump. As a result, your pulse rate will increase in an attempt to pump more vigorously.

As the organs and muscles receive less oxygen, you might also find that your breathing rate increases, as the brain tells the body it needs to increase its oxygen levels.

Feeling Dizzy or Seeing Stars

When your heart is pumping hard but your brain still isn’t getting enough oxygen in the blood, it can lead to dizziness or “seeing stars.”

The faster the heart pumps, the lower the blood pressure tends to drop, which can cause lightheadedness or the feeling of seeing light specks.

Difficulty Concentrating

As small as a 2 percent drop in fluid levels can impact cognitive ability. So one of the signs of serious dehydration is the ability to concentrate.

If you’re feeling distracted, all over the place, and like you can’t even focus on your run, dehydration may be to blame.

Muscle Cramps

Being properly hydrated is essential to maintain the body’s fluid and electrolytes balance. When you’re dehydrated, that balance becomes skewed, leading to muscle cramps.

Factors That Can Lead To Dehydration

While it’s always important to be aware of the possibility of dehydration, some factors increase the risk. Pay particular attention to the following.

Heat and Humidity

Running on hot and humid days makes you more susceptible to dehydration as you sweat more. Your body will likely work harder to cool you down, adding to your fatigue.

If it’s particularly hot or humid on the day, you’ll probably need to carry more water with you to stay hydrated.

Cold, Dry Air

Have you ever noticed your breath coming out in puffs when it’s cold? That’s water vapor escaping from your lungs. Unlike warmer air, there’s less moisture in cold air so you’re getting a little less moisture when you inhale, but losing more when you exhale.

This can contribute to dehydration as you may be losing more water than you realize when you’re exercising.

How Much You Sweat

Everyone is different, so nobody sweats the same amount. But how much you sweat will directly impact how much you need to drink to stay hydrated.

Not Drinking Enough

This is the most obvious one! If you’re just going for a short run, it might be tempting to leave the water at home. But even 15 minutes of running without replenishing your water can have adverse consequences—less in hot, humid weather.

How Far Can You Run Without Drinking Water?

There’s no proper answer to this question. It depends on all the factors we mentioned above—how hot it is on the day, how much you sweat, and how hydrated you are when you start running.

In realistic terms, you can run a full marathon without drinking water, but it will take a drastic and unpleasant toll on your body. It’s best to figure out the right time frame for you—it’s different for everyone—and stick to that if you want to perform at your best.

When to Drink and How Much to Drink

You should be sipping on water continuously throughout your run. But how do you know how much you should be drinking in total? The general rule of thumb is between 4 and 6 ounces every 15 to 20 minutes.

But that’s not optimal for everyone. It’s important that you find out what’s right for you so you can use it to your advantage! The first step is to calculate your sweat rate.

Calculate Your Sweat Rate

Doing the math here will help you land a number to aim for. This can be valuable, instead of just taking a bottle of water with you and hoping for the best!

You will need a scale, preferably a digital one. Also, make sure to weigh yourself nude, both before and afterward.

Here’s the calculation:

  • {[(pre-run weight- post run weight) x 16 ounces ] + ounces of fluid consumed during run} / hours spent exercising

Let’s see how this might look in the real world. Assume you weighed 150 lbs before your run and 148.5 lbs afterwards, you ran for 1 hour, and you drank 5 ounces of water.

Here’s how it would look:

  • {[(150 – 148.5) x 16] + 5} / 1 = 29

That shows a sweat rate of 29 ounces per hour. This means you should aim to consume around 7 to 8 ounces of fluid every 15 minutes in order to stay pretty well hydrated.

Water vs. Electrolyte Drinks vs. Sports Beverages

Water is the best way to start and all you need if your runs are limited to under an hour. If you’re running for more than an hour, it may be beneficial to use an electrolyte powder or tablet—these will prevent your fluid/electrolyte balance from becoming too skewed, which can lead to cramps and illness.

Sports drinks can be valuable on long runs, although you should be careful to choose one without excess sugar. Most sports drinks contain some carbs, which give you an extra boost of energy during your run as well.

Can You Drink Too Much Water?

Yes! Drinking too much water puts you at risk of something called hyponatremia—an abnormally low concentration of sodium in your blood. The balance can go out of whack when you drink too much water without replenishing electrolytes.

Hyponatremia can lead to a feeling of weakness, gastric distress, and muscle cramps. If you stick to your calculated water intake above, there’s little chance of going overboard, but be aware that it can happen.

Tips to Stay Hydrated on the Run

Ready to optimize your hydration? Try these tips!

Stay Hydrated Throughout the Day

Your run isn’t the only time you need to hydrate. You should be sipping on water throughout the day, preferably ending up with a total of between 8 and 12 cups per day.

Avoid Caffeinated Drinks

Caffeine can dehydrate you, so it’s wise to avoid caffeinated drinks as much as possible. One strong coffee or a caffeinated sports drink during a long run isn’t a problem but use them sparingly and wisely.

Drink Before You Run

Try to consume around 16 ounces of water in the hour or 2 before your run. Make sure you only really take in 6 to 8 ounces in the last 15 minutes before you start so you don’t have to stop off for the bathroom mid-run!

Plan Your Route

Carrying water can add unnecessary weight that can impact your performance on a run. If you’re a stickler for these kinds of things, plan your route so you can run past a water fountain and top up.

That way, you can carry half the amount of water you really need and just top it up quickly as you go past the fountain. 16 ounces weighs around a pound, which can make a big difference to your run!

Drink Regularly on Your Run

Rather than timing your drinking for every 15 minutes, try to sip regularly. That way, you don’t have to drink a whole gulp in one go, and you keep yourself hydrated without getting to the point of being thirsty.

Choose the Right Drinks for Your Run

Water is best if you’re running for less than an hour. Anything over that and you should definitely take an electrolyte supplement with you. You can opt for sports drinks if you’re running for a long time, but be aware of what’s in them.

Also, it’s a good idea to avoid caffeinated sports drinks, as they’re likely to dehydrate you more during your run.

Carry a Hydration Pack

If you want to make sure you’re carrying enough water without feeling lopsided and weighed down, you can invest in a hydration pack. This fits easily on your back and has a straw that you can sip on throughout your run.

It’s an easy, convenient, hands-free way of hydrating! It may take some getting used to, but it’s an excellent way of carrying a lot of water with you easily. For shorter runs you can use a handheld water bottle.

Photo of author


Ben is an avid road and trail runner, and has completed multiple marathons and ultras. A former running store owner, he now shares his knowledge and experience writing these articles.