Heat safety for runners and hikers

Why heat catches careful people out

Most outdoor problems announce themselves. You know when you have fallen, taken a wrong turn or been caught in a storm. Heat illness is different because it can affect the thing you need most to get yourself out of trouble: your judgment.

The National Weather Service lists confusion and slurred speech among the signs of heat stroke, and CDC NIOSH adds altered mental status, seizures and loss of consciousness. A runner or hiker on their own may not recognize those changes in themselves, and may not be able to make a phone call once they arrive.

So this guide covers two layers: preventing heat illness in the first place, and having a plan that still works if you cannot ask for help. Heat is only one season's risk; our seasonal outdoor safety calendar covers the rest of the year.

Heat cramps, heat exhaustion and heat stroke: signs and first actions

This is general information from US public health sources, not medical advice. If you have a heart condition, take medication that affects heat tolerance, or are unsure what is safe for you, talk to your doctor before exercising in hot weather.

Two details are easy to miss. First, the CDC lists both hot, dry skin and profuse sweating as signs of heat stroke, so someone who is still sweating can still be in danger. Second, the NWS says not to give fluids to someone with heat stroke. Cooling is the priority.

The first 10 minutes if someone overheats on the trail

Picture a July hike: your partner, climbing back up an exposed switchback at 1 p.m., slows, stumbles and starts talking nonsense about which way the car is. That confusion is the moment to act, not to push on for the trailhead.

If you are alone and you feel dizzy, nauseous or unusually weak, those same steps apply to you: stop, find shade, cool down, and tell someone where you are before things get worse. If you cannot describe your location, our answer on how to call 911 if you do not know where you are walks through what to say.

Timing: finish before the heat peaks

The simplest heat safety step is to avoid the hottest part of the day. Early morning is usually coolest, before pavement and rock have soaked up the sun. Evening can work, but surfaces stay hot after sunset and humidity often stays high.

On hikes, the problem is usually the return. A canyon trail that is shaded at 7 a.m. can be exposed and brutal on the climb out at 2 p.m. Set a turnaround time that has you finishing before the heat peaks, and keep it even if you feel strong. Our answer on staying safe hiking in the heat covers exposed terrain in more detail, and trail runners should read staying safe trail running in the heat.

If you move a run earlier to dodge the heat, you may be starting near dawn. Check sunrise with the Holler daylight tool and carry a light if it will not be fully light when you set off.

Water, pace and acclimatizing

Carry more water than you think you need, especially where there are no refill points. Build the route around water you know exists, such as fountains, shops or a loop past your car, rather than hoping to find some. On a hike, carry enough for the return leg, which is often hotter than the walk in.

Slow down. Your usual pace takes more effort in heat and humidity, so run by effort rather than by the watch. Walk breaks are a legitimate tool, not a failure.

Your body adapts, but not instantly. The CDC Yellow Book says that with a suitable amount of daily exercise, most acclimatization changes occur within 10 days, and that the adaptation fades within days to weeks without heat exposure. That matters at the start of summer, during an early-season heat wave, after a cool spell, and when you travel somewhere hotter than home. Make those first days short and easy.

Wear light-colored, loose, breathable clothing and a hat, and use sunscreen.

Why a return time matters most in the heat

Heat illness can leave you unable to call for help. You might sit down in the shade to recover and not get up, or become confused about where you are. In that situation, the most useful safety tool is someone who already knows when you should be back.

Holler cannot sense heat illness or measure your temperature. What it can do is notice that something may be wrong. Set an optional return time when you start; if you have not checked in five minutes after it, Holler's server sends your Guardians an overdue alert, even if the app on your phone is closed. You can also turn on a stationary alert: if you stop moving for the time you choose, Holler asks "Are you OK?" and alerts your Guardians if you do not answer.

Your Guardians open your live link in any web browser, with no app or account, and see the route you have travelled and your latest or last known location. That gives them something concrete to tell 911 if they cannot reach you. Share when to worry if someone is late back from hiking with them before summer.

Keep the return time realistic. In heat you will move more slowly, so add a buffer. An alert should mean something may be wrong, not that you took an extra water break.

Before a hot run or hike

A short routine before you head out covers most of what matters.

Gear worth carrying

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