HOW TO KEEP COOL AND HYDRATED WHEN RUNNING IN THE HEAT

Published: 30/06/2026 | By: Priya Gopaldas

Hot weather can make even your easiest run feel harder than it should. In this guide, doctor and running ambassador Priya Gopaldas shares the simple changes that can make all the difference – from staying hydrated and replacing electrolytes to keeping cool and knowing when it's time to call a run early.

As a runner who's trained through everything from freezing winter mornings to marathon blocks in the middle of summer, I've learnt the hard way that hot-weather running requires a slightly different approach. Some of my toughest training runs haven't been on hills or during races – they've been on hot, humid days when a pace that normally feels comfortable suddenly feels impossible.  

If you've ever looked down at your watch and wondered why you're running slower despite trying harder, the heat may well be the reason.  

When we run, our muscles generate heat. To stop us overheating, the body has a built-in cooling system: we sweat, blood flow increases to the skin, and our heart works harder to help get rid of excess heat. The problem is that when it's already hot outside, that cooling system must work much harder. 

Your heart rate often rises, you lose more fluid through sweat, and your body has to divert energy towards staying cool rather than powering your run. That's why running in hot weather can leave you feeling more fatigued, even if you're covering the same distance at a slower pace. 

As runners, we often focus on pace, but in hot conditions, effort is usually the more useful metric. I've had summer runs where my watch tells me I'm running 20-30 seconds per km slower than normal, yet it feels just as hard as a race effort. That's completely normal (even for experienced runners who find themselves slowing down significantly during hot weather sessions).  

What’s important is to never ignore signs of overheating. Dehydration, heat exhaustion, dizziness, muscle cramps, fatigue, and in severe cases heat stroke can all occur when the body struggles to regulate temperature effectively. 

How to Stay Hydrated When Running in the Heat

One of the most common mistakes I see runners make is trying to catch up on hydration right before a run.

Aim to drink regularly throughout the day rather than immediately before a run as if you start a session already dehydrated, it can make overheating much more likely.

For runs lasting less than an hour, many runners can usually manage with good pre-run hydration. However, during longer sessions, particularly over 60-90 minutes, you'll likely need to drink during the run.

Your exact fluid requirements depend on factors including:

• Temperature and humidity

• Sweat rate

• Body size

• Running intensity

• Duration of exercise

After your run, continue replacing fluids gradually over the next few hours. A useful guide is checking urine colour – pale yellow generally suggests good hydration, while darker urine may indicate dehydration.

Personally, if I'm heading out for a long run in summer, I almost always take a hydration vest with soft flasks. It's far easier than trying to plan routes around water fountains and means I can drink little and often.

Options include:

• Hydration packs or running vests (my favourite is the Salomon Active Skin, had the same one for years!)

• Handheld water bottles

• Running belts with bottle storage 

• Soft flasks (I sometimes run with one of the Salomon flasks from my running vest if my run isn’t too far)

The best choice is the one you'll actually use.

Electrolytes and sweat loss 

When we sweat, we lose electrolytes too – particularly sodium, but also potassium and other minerals that help our muscles and nervous system function properly. 

If you're doing a longer run, a hard session, or you're someone who sweats heavily, plain water alone may not always be enough. 

That's where electrolyte tablet/powders or sports drinks can be useful. Replacing both fluid and sodium can help reduce the risk of cramps, fatigue, and that horrible washed-out feeling many runners get after a long hot run.  

During long runs in the heat, I tend to carry salt tablets in my running vest (which I take regularly) and have 2 soft flasks – one with water and the other with water and electrolytes.  

Signs You Might Be Dehydrated 

Learning to recognise dehydration early can prevent more serious problems developing. 

Keep an eye out for: 

• Headaches 

• Dizziness 

• Fatigue 

• Dark urine 

• Muscle cramps 

• Dry mouth 

• Unusually high heart rate 

• A sudden drop in performance 

If any of these signs start appearing, it's often your body's way of asking for a break and some fluids. If you’re in the middle of a long run, I’d recommend slowing down, finding a shaded area, re-hydrating and assessing how you feel before deciding whether to carry on your run.  

For more info on electrolytes (as knowing how much/ what electrolytes we need can be complicated!) here’s the link to my previous blog post explaining all about electrolytes.  

How to Keep Cool While Running  

Choosing the right clothing can make a significant difference. 

Look for lightweight, breathable, moisture-wicking fabrics designed specifically for running. Technical fabrics help move sweat away from the skin, allowing it to evaporate more efficiently. 

I always recommend avoiding cotton for summer runs, as it absorbs sweat and can feel heavy and uncomfortable. 

Light-coloured clothing can also help reflect sunlight and reduce heat absorption. 

Accessories to Your Advantage 

A few simple accessories can make a surprising difference: 

• A lightweight running cap/visor (shades your face and eyes from direct sunlight) 

• UV-protective sunglasses (protects eyes from UV rays and pollen)  

• Sweatbands (absorbs sweat before it runs into eyes)  

• Cooling towels (can be dampened and placed around the head/neck to cool down)  

In the heat I always carry a buff. It’s multifunctional- I use it as headband to prevent sweat stinging my eyes and if it gets really hot, I can soak it in water to help keep my head/neck cool and as I suffer from hay fever, I can use it to cover my nose/mouth in high pollen areas.  

Sun protection strategies 

As runners, we often spend hours outside and don't always think about sun protection until it's too late. 

Apply sunscreen before every run, particularly on exposed areas (face, ears, neck, shoulders, legs) and consider taking a small bottle with you if you're heading out for a particularly long session/ sweating heavily.  

Sunburn doesn't just damage your skin – it can also make recovery harder and place additional stress on the body. 

Cooling techniques during runs:  

Some of the simplest cooling strategies are often the most effective. 

Try: 

• Pouring water over your head or neck 

• Running through shaded sections of your route 

• Choosing routes near rivers, lakes, or the coast 

• Taking short cooling breaks if needed 

I've lost count of the number of summer runs where pouring cold water over my head halfway through completely changed how I felt. 

 

Training Smart in Hot Conditions 

 One of the biggest mistakes runners make is trying to maintain the same pace they run in cooler weather. 

 Adjust Your Expectations 

When temperatures rise, slowing down isn't a sign of losing fitness- it's often the smart thing to do. I frequently use effort rather than pace as my guide during summer training. If your usual easy run suddenly feels much harder, your body is giving you useful feedback. 

 Plan Your Timing 

Early morning or late evening runs are often significantly cooler than midday sessions. Whenever possible, avoid the hottest part of the day and choose shaded routes, trails, or routes with access to water. 

 Stay Flexible 

Sometimes the safest option is moving a session indoors. A treadmill workout, gym session, or cross-training workout may be a better choice than forcing an outdoor run during extreme heat or humidity. 

 Prioritise Recovery 

Running in the heat places extra stress on the body. 

You may find you need: 

• Additional rest days 

• More sleep 

• Increased fluid intake 

• Reduced training intensity 

Listening to your body is one of the most important summer running tips I can give. 

Acclimatising to Running in the Heat 

The good news is that your body gets better at coping with heat over time. 

With repeated exposure over 1-2 weeks, heat acclimatisation occurs. Your body becomes more efficient at cooling itself, sweat production improves, and cardiovascular strain may reduce. The key is gradual exposure. 

Build heat tolerance safely by: 

• Increasing exposure slowly 

• Monitoring hydration 

• Tracking recovery 

• Paying attention to heart rate 

• Using perceived effort rather than pace 

During this period, it can be helpful to focus less on performance metrics and more on how your body feels. 

Warning Signs: When to Stop Running 

 Every runner should know the warning signs of overheating. Stop and seek shade if you develop: 

• Dizziness 

• Nausea 

• Headaches 

• Chills 

• Muscle cramps 

• Confusion 

• Extreme fatigue 

If you feel unwell, don't try to push through it. 

Move to a cool or shaded area, drink fluids, loosen clothing, and begin cooling the body. If symptoms are severe, worsening, or include confusion, seek urgent medical attention as heat stroke can be a medical emergency.  

And remember there are some days when skipping or postponing a run is simply the right call. During extreme heat or humidity, even very fit runners can struggle. 

Running Gear and Hydration Essentials for Summer 

Having the right kit can make summer running far more comfortable, especially when temperatures start to climb. Staying hydrated should be the priority, and for longer runs, a hydration vest such as the Salomon Active Skin 4L is a practical choice, allowing you to carry plenty of water without restricting movement. On shorter outings, adding electrolytes to your water can help replace the salts lost through sweat, with O.R.S. hydration tablets being a reliable option.

Choosing lightweight, breathable clothing is equally important, and I particularly rate the Nike AeroSwift running vest, which offers excellent ventilation to help keep you cool.

 Finally, don't overlook sun protection – wearing sunglasses, applying sunscreen before you head out and using a running cap can all make a noticeable difference when you're spending time in the summer sun. 

Final Thoughts 

My approach to summer running is simple: respect the heat. You don't need to fear running in the heat, but you do need to adjust your expectations. Slow down when needed, stay on top of your hydration, replace electrolytes during longer sessions, prepare with appropriate clothing and listen to what your body is telling you. 

The runners who train best through summer aren't necessarily the ones who push hardest- they're often the ones who listen to their bodies, stay hydrated, and adapt intelligently to the conditions.