Is It Safe to Exercise Outside Today? This Chart Can Help You Decide

Yahoo

17-07-2025

If this summer feels super warm to you, that's probably because it is. Crazy-high temperatures in a lot of the country are the new normal, thanks largely to climate change. In fact, June 2025, was the third-warmest since record-keeping began in 1850, according to the National Centers for Environmental Information. The period from January to June 2025 was the second-hottest first half of the year ever.
Unfortunately, it doesn't look like these high temps are going to go down any time soon. In May, the World Meteorological Organization issued a statement saying that temperatures are expected to stay at or near record levels for the next five years.
The heat is not just uncomfortable — it can be downright dangerous. The most recent figures show that heat-related illnesses contribute to more than 1,000 Americans every year, according to the EPA. In some instances, heat stroke may kill someone and in other cases, certain existing conditions may be exacerbated by the high temperature.
What that means to folks who stay fit by walking, running, biking, playing pickleball or doing anything else under the sun: a greater chance of being hit by heat exhaustion or one of the more serious health calamities brought on by high temperatures, says Elizabeth Gardner, M.D., a sports medicine expert and an associate clinical professor at Yale School of Medicine.
'It certainly is a paradigm shift, but this is where we're at,' says Dr. Gardner, of the fact that we all have to do more to guard against heat exhaustion, heat stroke and other issues, even if we're used to working out in warm climates.
How hot is too hot to work out?
Google that question, and you'll get a big '90°F' up at the top of the search results, but that's just an estimate and only part of the story.
'The problem with that number is that it doesn't take into account the other factors that affect your body's perception and experience with heat,' says Dr. Gardner. 'We all know that 90° temperatures and 90% humidity in Connecticut or the Bahamas is not the same as 90° in Arizona with dry heat. It feels different, and the body is being stressed in different ways.'You can reference the Heat index from the National Weather Service above, which combines the humidity with the temperature to give what the temperature feels like for your body. For instance, if the temperature is 90°F and the humidity is 70, you've entered the dangerous zone of 105°F, which means you may be susceptible to heat-related illnesses. You can also use its calculator to help you.
But if the only info you have is the temperature, 80° to 90°F is the be-extra-careful zone, says Stefani Sassos, M.S., R.D.N., C.S.O., C.D.N., NASM-CPT, the Good Housekeeping Institute's Nutrition Lab Director, who is also a personal trainer. 'There are a lot of variables, so it's hard to pin it down to just a number.'
Other factors to consider
The humidity
Why? Because sweating is the main way your body cools itself down when you expend energy. If the air contains a lot of moisture — i.e., if it's humid — the sweat doesn't evaporate as quickly (or at all) and you don't cool down. 'You just keep sweating and getting dehydrated, and you're still not able to get rid of the heat,' says Dr. Gardner.
And low humidity is differently tricky — your sweat evaporates quickly, which means you cool down quicker, which is good. 'But in dry heat the sweat evaporates so quickly that you don't even notice it, which means you don't see the telltale sign that you need to hydrate,' says Sassos. You can, in fact, get dehydrated really easily in dry heat (or when you're swimming), even if you don't seem to sweat.
The heat index (which factors in heat and humidity) or the 'feels like' temperature on your phone's weather app is an at-a-glance way to get a better idea of what it will feel like outside, though sports medicine health professionals use the 'wet bulb' gauge, which also takes into account wind speed and cloud cover.
Your fitness level
It is true that people who are in better cardiovascular shape tend to be able to withstand exercise in the heat better than those who are just starting out, Dr. Gardner says, but that, too, only goes so far. 'You can have someone who is very fit at running on the treadmill in air conditioning at the gym, and she does the same workout, or even less, in a very different temperature or with different humidity conditions, and that same person can be at risk for heat illness,' she says. 'Your body is used to handling that physiologic muscle stress, but you haven't had to incorporate the thermo-regulatory effect in the same way.'
In other words, the system that works at cooling you down when you expend energy may not be as 'in shape' as your heart and lungs and muscles.
Your age
Children and people 65 or older are at greater risk for heat illness, according to the Centers for Disease Control and Prevention.
Your overall health
'People who have an underlying medical condition or a current illness, their bodies are not as equipped to handle more stress in general,' says Dr. Gardner.
Day-to-day factors
These include how tired you are, whether you're stressed out, if you've eaten well and have taken in enough water in the last 24 hours or whether you had too much alcohol to drink last night. 'We all can feel different on a daily basis, so the things that affect how you wake up feeling in the morning can really affect your body's physiology,' says Dr. Gardner. 'You are in your same human body, in the same physical shape from day to day, but that doesn't mean your body is able to respond to the stress brought on by the heat equivalently day to day.'Follow these steps to stay safe in the heat:
Trust your body. 'If you go outside, and it just feels borderline uncomfortable, you should say 'I'm just going to do a light workout' or go indoors,' says Sassos.
Think about your body's ability to handle stress that day. Things like if you're tired, under the weather, didn't sleep well or are a little hungover all affect how well your body will handle the heat that particular day. 'You want to leave a little in the tank to live to fight another day — there's always tomorrow,' she says. 'That's not to say you should trade your sprint workout in 100° weather for sitting on the couch, but there are lots of other ways to get the benefits of working out.' Think: Indoor cardio, Crossfit or yoga (not the hot kind) or go for a swim.
Work out early in the morning or in the evening. This is when it tends to be cooler. 'Avoid the middle of the day,' says Sassos.
Wear wicking clothes. Lightweight performance clothes designed for sports in hot weather are key, along with a hat, shades and sun protection. 'Don't go in your old college t-shirt, which has zero wicking capacity,' says Sassos. But be aware: 'Not all fabrics that claim to be moisture wicking actually are,' says Lexie Sachs, the Good Housekeeping Institute's Textiles, Paper & Apparel Lab executive director. 'My trick is to take a drop of water and place it on the inside of the fabric — the part that touches your skin. You should see that drop spread out wide quickly. If it beads up or doesn't spread, then it won't manage your sweat well.'
Hydrate before, during and after your workout. 'Obviously, after is crucial, but try to bring a bottle with you,' says Sassos. If it's super hot, or you're exercising for more than an hour, sip an electrolyte drink.
Don't push it. 'In high heat, try taking it a little easier, really gauging how your body feels and being okay with turning back a little sooner,' says Dr. Gardner.
Know the signs of heat illness. If you don't feel right, stop and get someplace where you can rest, hydrate and cool down, says Sassos.
The warning signs of heat exhaustion include the following, according to the :
Heavy sweating
Paleness
Muscle cramps
Tiredness
Weakness
Dizziness
Headache
Nausea or vomiting
Fainting
Untreated heat exhaustion can progress to heat stroke, which can lead to permanent disability or death if not treated quickly. If you see someone with these signs, call 911 and move the person to a shady area and try to bring their temperature down as quickly as possible.These are some of the warning signs of heat stroke:
A body temperature above 103°F
Red, hot, and dry skin that isn't sweating
A Rapid, strong pulse
Throbbing headache
Dizziness
Nausea
Confusion
Unconsciousness
Bottom line
Heat illness is no joke, so pay attention to your body and be open to working out indoors if need be.
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