Everything to Know About Running in the Heat

There are two types of runners: those who love nothing more than to push through a hot, sweaty run and those who don’t. No matter which type of runner you are, running in the heat requires specific knoweldge about how the body responds to both temperature and humidity. Here is everything you need to know about running in in the heat in order to prevent common heat-related illnesses and ailments.

Run early or late: Don’t do long or higher-intensity workouts during the heat of the day. If you must run at midday, pick routes with some shade. Also, start your workout slower than you usual. If you feel good halfway through, it’s okay to speed up a little bit.

Dress for the weather: Wear apparel that’s light in color, lightweight, and has vents or mesh. Microfiber polyesters and cotton blends are good fabric choices. Also, be sure to wear a hat, shades, and sunscreen with an SPF of 30 or higher.

Learn the details about your meds: Antihistamines and antidepressants can have a dehydrating effect. Using them just before a run can make you have to pee, compounding your risk of dehydration.

Drink water early and often: Top off your fluid stores with 16 ounces of sports drink an hour before you head out. Then, toss down five to eight ounces of sports drink about every 20 minutes while working out. Sports drinks beat water because they contain electrolytes, which increase your water-absorption rate, replace the electrolytes you lose in sweat, and taste good, making it easy to drink more.

Think twice about drinking alcohol: if you want to cool off with a cold beer after your run, know that only small studies have found that it’s okay to have alcohol after exercise. This 2015 study in the Journal of the International Society of Sports Nutrition looked at 16 men who drank beer (or didn’t) after dehydrating exercise. There was no difference in the rehydration strategies between groups. Still, a 2021 systematic review of beer and exercisre found that the data is inconclusive given that people drink and eat differently in real than they do in labs. Therefore, runners should not make “sweeping conclusions” about drinking beer postrun.

Be patient: Give yourself eight to 14 days to acclimatize to hot weather, gradually increasing the length and intensity of your training. In that time, your body will learn to decrease your heart rate, decrease your core body temperature, and increase your sweat rate.

Seek grass and shade: It’s always hotter in cities than in surrounding areas because asphalt and concrete retain heat. If you must run in an urban or even a suburban area, look for shade—any park will do—and try to go in the early morning or late evening.

Check the breeze: If possible, start your run going with the wind and then run back with a headwind. Running into the wind has a cooling effect, and you’ll need that in the second half of a run.

Head out early or late: Even in the worst heat wave, it cools off significantly by dawn. Get your run done then, and you’ll feel good about it all day. Can’t fit it in? Wait until evening, when the sun’s rays aren’t as strong—just don’t do it so late that it keeps you from getting to sleep.

Slow down: Every 5°F rise in temperature above 60°F can slow your pace by as much as 20 to 30 seconds per mile. So don’t fight it—just slow down.



Run in water: Substitute one weekly outdoor walk or run with a pool-running session of the same duration. If you’re new to pool running, use a flotation device and simply move your legs as if you were running on land, with a slightly exaggerated forward lean and vigorous arm pump.

Heat Cramps

Cause: Dehydration leads to an electrolyte imbalance
Symptoms: Severe abdominal or large-muscle cramps
Treatment: Restore salt balance with foods or drinks that contain sodium
Prevention: Don’t run hard in the heat till acclimatized, and stay well hydrated with sports drink

Heat Fainting

Cause: Often brought on by a sudden stop that interrupts bloodflow from the legs to the brain
Symptoms: Fainting
Treatment: After the fall, elevate legs and pelvis to help restore bloodflow to the brain
Prevention: Cool down gradually after a workout with at least five minutes of easy jogging and walking

Heat Exhaustion

Cause: Dehydration leads to an electrolyte imbalance
Symptoms: Core body temperature of 102° to 104°F, headache, fatigue, profuse sweating, nausea, clammy skin
Treatment: Rest and apply a cold pack on head/neck; also restore salt balance with foods and drinks with sodium
Prevention: Don’t run hard in the heat till acclimatized, and stay well hydrated with sports drink

Hyponatremia

Cause: Excessive water intake dilutes blood-sodium levels; usually occurs after running for four or more hours
Symptoms: Headache, disorientation, muscle twitching
Treatment: Emergency medical treatment is necessary; hydration in any form can be fatal
Prevention: When running, don’t drink more than about 32 ounces per hour; choose sports drink over water

Heat Stroke

Cause: Extreme exertion and dehydration impair your body’s ability to maintain an optimal temperature
Symptoms: Core body temp of 104° or more, headache, nausea, vomiting, rapid pulse, disorientation
Treatment: Emergency medical treatment is necessary for immediate ice-water immersion and IV-fluids
Prevention: Don’t run hard in the heat until acclimatized, and stay well hydrated with sports drink

Blisters, chafing, and sunburn can strike anytime, but they’re more common in hot weather. Here’s how to treat these problems and to prevent them from occurring in the first place.

Black toenails

Lots of downhill running and too-small shoes can bring these on, as both cause your toes to slam into the front of your shoe. Wear properly fitted shoes and trim your nails regularly. Once you have a black toenail, there’s not much you can do. It’ll usually heal on its own within a few months. If it’s really painful, see a podiatrist, who may drain the fluid from under the nail.

Blisters

These are caused by friction, excessive moisture (sweaty feet, wet weather), or shoes that are too small, too big, or tied too tight. So be sure to buy properly fitted shoes. Because your feet can expand a half size over a day, shop in the late afternoon or evening. Putting Vaseline, sports lube, and bandages over blister-prone spots may also help. Ignore blisters smaller than five millimeters (the size of a pencil eraser), since they’re usually not painful. But pop the big ones. With a sterile needle, prick the side of the blister and drain it. Don’t remove the top of the blister; instead, cover it with an antibiotic ointment and moleskin or a bandage.

Chafing

Skin-to-skin and skin-to-clothing rubbing can cause a red, raw rash that can bleed, sting, and make you yelp during your postrun shower. Moisture and salt on the body make it worse. Underarms, inner thighs, along the bra line (women), and nipples (men) are vulnerable spots. To help prevent it, wear moisture-wicking, seamless, tagless gear. Fit is important—a baggy shirt has excess material that can cause irritation; a too-snug sports bra can dig into skin. Apply Vaseline, sports lube, Band-Aids, or NipGuards before you run. To treat chafing, wash the area with soap and water, apply an antibacterial ointment, and cover with a bandage.

Muscle cramps

The best way to prevent these is to be well trained, because fatigue seems to be the main reason for cramping in races and hard workouts. Plyometric training (bounding, hopping) may lower your risk as well, and so may keeping well hydrated with a salty drink. If a cramp hits, stretch immediately. If your calf cramps, for instance, stop running, straighten out your leg, pull back on your toe, and hold the stretch for several seconds. You may need to continue this for 2 to 3 minutes. Then massage the muscle to help ease the pain and get you ready to run again.

Sunburn

To lower your risk, avoid the sun between 10 a.m. and 4 p.m., wear a hat, run in the shade, and wear sunscreen. Because sunscreen can’t withstand prolonged exercise, stash some in your pocket or circle back to your car so you can reapply every hour. You can also wear technical apparel that blocks UV rays. If you get sunburned, taking an anti-inflammatory and applying aloe vera a few times per day will take the edge off the pain.

Finally, be aware of the heat index, which calculates the effect on your body of both the heat and the humidity. The chart lets you know whether or not it’s safe to be outside. Forget about running when the heat index is high. Instead, get on your treadmill or do another cardio, strength, and flexibility/balance workout—indoors.