What is Dew Point and How Will It Affect Your Run?

As the spring season transitions into the long, warm, sun-filled days of summer, your fellow runners’ Facebook, Instagram or Strava posts will no doubt begin mentioning temperature and humidity to indicate the challenges they experienced on their run. But how many people do you see mentioning dew point?

Dew point is the most objective measure of the level of water in the air, which gives you more information than any other metric about how sticky or dry it feels outside. Unlike humidity, which can feel amazing in 55 degree weather and awful in 85 degrees, dew point is an absolute measurement that lets you know how difficult a run will feel, whether you drank enough water and if that running singlet is one layer too many. You can find the dew point on most weather apps or weather websites.

Most runners are familiar—or rather, overly familiar—with the concept of sweat. It’s the body’s natural mechanism for cooling off, and if you combine that moisture on the skin with a nice breeze, life can be pretty good. But in many regions, high heat comes with a high dew point, meaning the air is already so filled with water, it’s difficult for sweat to evaporate off your skin.

In technical terms, dew point represents the temperature when air, at a given atmospheric pressure, reaches saturation point and can no longer hold onto moisture. The higher the dew point is, the more saturated the air is with water. Therefore, dew point doesn’t just affect the body’s attempt to self-regulate its temperature through sweat, it also affects the amount of oxygen you get in each breath.

You may have heard how tough it is to run at high altitude, and running in a high dew point poses a similar challenge. Both high elevation and high saturation lower the density of oxygen in the air, making it feel harder to breathe. In effect, a high dew point might as well be a jaunt in the Rocky Mountains, but without the cool weather and beautiful trails.

The good news is that it’s not common to come across both high elevation and high dew point, since higher elevation means decreased barometric pressure, which decreases dew point.

While there are handy charts about running in a high dew point (see below), the effects of dew point on athletics are understudied and inconclusive. Meteorologists and Climatologists Andreas Matzarakis and Dominik Fröhlich pointed out how the effect of weather on sports events has not been well studied through the 2000s. Now that global sports events are considered in extreme-weather condition-areas, such as the 2019 Track and Field Championships in Qatar and the upcoming 2022 FIFA World Cup, people are more interested in the effects of high dew point and other weather conditions on athletes.

Check out this chart from Runner’s World about running and dew point.

On the other hand, a 2012 analysis of over a million marathoners by Nour El Helou, et al., concluded that there’s only a weak association between dew point and running performance. So just because the weather prediction includes a high dew point, that doesn’t mean you have to completely scratch your running goal.

While it’s never fun to slog through a muggy workout, humans are able to adapt. In fact, a 2020 research projectconcluded that humans have evolved more than other animals to run in heat and other difficult weather conditions. Just like people can adjust to heat, cold and higher elevations, they can also adjust to high dew points. Some people may also be predisposed through genetics and environment to feel less uncomfortable than others in certain conditions. All of this means that, when it comes to dew point, you can adapt and overcome.

While you can adjust your race goals on a sultry summer day— you know, the ones where you walk out the door and a film of moisture instantly develops on your skin— don’t let it get in your head. Instead, focus on the elements you can control.

Hydrating properly goes a long way when running in high dew point. It also helps to reduce your alcohol consumption and drink more water. We know that a post-run bubbly beer on a hot summer day is pure bliss. However, it can also set you up for major dehydration when you trade H2O for suds. Dehydration not only curbs recovery from the run you just finished, but it also sets you up for a sub-par run the next day. And, did you know that even slight dehydration impairs mental capacity? So, drink more water throughout the summer, so you have better runs, experience enhanced recovery and function optimally at work. Win-win-win.

You should also carry hydration and plan your routes based on water availability. Getting stuck on a run with no water when you’re thirsty and near bonking is perhaps one of the worst things. Ever. OK, maybe that’s a little dramatic. But still, it sucks. If it’s summer, carry water every time you run, or at the very least take a bottle to stash somewhere along your route (if you’re doing an out and back). It's also a good idea to plan your run according to available water stops so that you can drink from a fountain and refill your bottle or pack. Don’t ever hesitate to stop and slurp; running without drinking water doesn’t make you tougher.

Dressing appropriately can combat heat and sweat effectively–simply wear less clothing. Yep, shed the layers and let your skin breathe. Opt for shorts and tank tops (or no tops if you dare). Make sure your layers are lightweight, light in color and breathable. Also, choose fabrics with sun protection and wear them in combination with sunscreen and sunglasses. Yes, sunscreen is a must.

Don't just change your hydration and wardrobe, though. Change your mindset and set your pride aside before heading out the door. One suggestion is to focus on total run time rather than the distance or pace. While mental math is unavoidable on the run, switching your focus from distance to time will keep you from comparing your regular paces to your heat-adjusted ones.

Listen to your body. Keep an eye on your heart rate and other stress indicators. At the end of the run, you’ll gain satisfaction knowing you did your best.

If you still have to get a harder run in, try running early in the day and avoid the sun as much as you can by picking a shaded route. Stay cool by sticking some ice cubes under your hat or even in your shorts or sports bra.

The bottom line is that no one is immune to the effects of weather during a run. However, just like you can prepare for heat, hills and elevation, you can adapt to a high dew point with the right training and mindset. Always be sure to take the normal safety precautions in high heat and humidity.