Tag: Sweating

How to Exercise in the Summer Heat

As record high temperatures batter much of the country, expert advice on staying active this summer.

The summer of 2021 came in sizzling, with June temperatures in many parts of the United States shattering records, baking landscapes and prompting those of us who usually exercise outside to question when, how — and if — we should continue to work out in nature’s furnace.

Helpfully, a group of exercise scientists wrote a comprehensive scientific review about training and competing in scorching heat, in preparation for the upcoming Summer Olympics in torrid Tokyo. Published in the aptly titled journal Temperature, the review focuses on elite athletes — but, the authors agree, the advice can be adapted for those of us training for a summer fun run or charity bike ride or aiming simply to stay active and safe outside until fall. What follows is a compilation of their expert recommendations, including when to down a slushie, why you might want to take a hot shower and whether to freeze your underwear.

It’s Too Darn Hot, So Be Strategic

When we exercise, we generate internal heat, which our bodies shed by sweating and shunting warmed blood away from our cores and toward the skin. If ambient temperatures rise, though, this process falters. Body heat builds up. Our hearts labor to send additional blood toward the skin. We glisten with sweat, and the same run, stroll or ride that felt tolerable during cooler weather now drains us.

To sidestep these conditions, we can move our workouts indoors, into air-conditioned comfort, or schedule them strategically. “I would always recommend the morning,” especially for city dwellers, says Oliver Gibson, a senior lecturer in exercise science at Brunel University London and lead author of the review. “In an urban area, it is likely that the concrete will have retained a high amount of residual heat that will radiate back” at exercisers later in the day, he says. Unshaded sidewalks similarly will be hotter than parks and leafy pathways.

Aim for Acclimitization

We also should accustom ourselves, slowly, to unfamiliar swelter, Dr. Gibson says, a process known to exercise scientists as acclimatizing, which involves working out sometimes, by choice, when the day is warmest. This approach helps to condition our bodies to better cope with the heat. Once acclimatized, we will sweat earlier and more abundantly than before, dissipating internal heat better and leaving us feeling bouncier and less fatigued.

Acclimatizing should be gradual, however. To start, slather on sunscreen, fill a water bottle, head outside after about 10 a.m., when temperatures intensify, and try to complete a gentler version of your standard workout, says Carl James, a senior physiologist at the National Sports Institute in Kuala Lumpur, Malaysia, and co-author of the review. If you usually run for 30 minutes, for instance, maybe jog for 20, and monitor how you feel. If your heart seems to be racing, he says, or you feel lousy, “slow down.”

After a few acclimatization sessions, you should notice your clothes and skin are drenched, Dr. Gibson says. Congratulations. “Earlier and more profuse sweating is a great sign that heat adaptation is taking place,” he says. Most of us acclimatize after about five to 10 hot workouts, he adds, although women, who tend to sweat less freely than men, may require an extra easy session or two to be fully prepared for harder workouts in the heat.

Take a Warm Soaking

After each acclimatization session, head for the showers, but dial up the heat. Standing under a warm shower spray or soaking in a hot bathtub for 10 minutes or so after a sweltering workout prompts our bodies to continue acclimatizing, Dr. Gibson says. “It extends the stimuli for heat adaptation,” he points out, “and is therefore welcome and beneficial.”

Slurp a Slushie Beforehand, Consider Cold Underwear

An icy beverage before a hot workout “will help with hydration and provide a combination of perceptual and actual cooling,” Dr. Gibson says. Aim to drink about 16 ounces of cold fluid 20 minutes or so before you head out. Drinking closer to the session’s start could cause stomach upset during your workout.

Slapping a cold washcloth onto your neck, donning an ice vest or slipping into athletic undergarments that have spent the night in the freezer likewise can up coolness (if not comfort) during hot-weather exercise. So can a gentle misting of chilly water on your face or licking an ice pop, says Ashley Willmott, a lecturer at Anglia Ruskin University in Cambridge, England, and another review co-author.

But these techniques can be risky, too, he cautions, because the cooling effects are limited and short-term, and potentially deceptive. “We sometimes see people cool before exercise, feel great, then head out too fast or hard,” he says, winding up prematurely winded and possibly on the cusp of heat problems.

Recognize Signs of Overheating

If you feel nausea, headache, dizziness or cramping during a hot workout, slow down or stop and hunt for shade, Dr. Gibson says. These could be signs of incipient heat illness. (You can learn more about the symptoms of heat illness and heat stroke at the website of the Centers for Disease Control and Prevention.)

Unfortunately, heat illness also clouds thinking, says Neil Maxwell, a lecturer in environmental physiology at the University of Brighton in England and the review’s senior author. “Your judgment becomes impaired,” he says, and you may not realize you are overheating.

He and his co-authors strongly recommend exercising with a partner in the heat. If either of you starts to feel “seriously hot or shows signs of cognitive dysfunction,” he says, such as sudden confusion, get off the path, under a shady tree or awning, and call for help. “Rapid cooling is essential within the first 30 minutes” of such an episode, Dr. Maxwell says. Immediately applying a cool cloth could help to start lowering body temperature.

You might also protect yourself and your training partners by the simple expedient of rejiggering your routes, Dr. Gibson says. “On hot days, do shorter loops” than normal and include “a dedicated water station,” he suggests, such as a public drinking fountain. Refill your water bottle there or stick your head under the flow each time around. Plus, “if you are feeling the heat,” he concludes, running in short loops “makes ending the session early more realistic.”

Are Natural Deodorants Better for You?

Much of the marketing suggests that they’re safer than more traditional underarm products, but that hype is not based on science.

Google “natural deodorant” and you’ll find countless articles detailing all the reasons you should buy them. Some claim that the aluminum in most conventional antiperspirants can lead to Alzheimer’s disease or cancer. Others assert that certain ingredients in traditional deodorants and antiperspirants are “toxic,” or that they can kill off the “good” bacteria in your armpits.

Many natural deodorant companies have seized on these perceptions, implying in their marketing that the ingredients in conventional deodorants are the “stuff you don’t want,” and that what you do want is their “natural” product that is made from “plant- and mineral-based odor fighters” and “clean ingredients.”

But experts, including an oncologist, an epidemiologist, a skin microbiome expert and several dermatologists, said that there is no definitive evidence that regular deodorants or antiperspirants are worse for your health than natural deodorants. In fact, they said, they’re perfectly safe.

And while natural deodorants might contain seemingly healthier ingredients than your conventional drugstore antiperspirant, they can still have substances that might irritate your skin. In the end, the experts said, the way a deodorant makes you feel (and smell) should guide your decision to use it.

Are natural deodorants better for you?

No. One of the biggest and most alarming false claims made about conventional antiperspirants is that they cause breast cancer — a rumor that began with an email chain letter from the 1990s. It said that antiperspirants, which minimize perspiration by blocking sweat ducts, prevent the armpit area from “purging toxins,” which could build up in “the lymph nodes below the arms” and cause cell mutations and ultimately breast cancer. The letter also claimed that razor nicks from shaving could further increase breast cancer risk by allowing chemicals from antiperspirants to enter the body.

This, say experts — including those from the American Cancer Society — is false. “To date, there’s absolutely no evidence that breast cancer is caused by exposure to anything in antiperspirants or deodorants, full stop,” said Dr. Harold Burstein, a breast oncologist at the Dana-Farber Cancer Institute and professor of medicine at Harvard Medical School.

The same goes for another cancer-related rumor, which is that the aluminum from antiperspirants could be absorbed into the skin and increase breast cancer risk by altering breast cell estrogen receptors. Again, Dr. Burstein said, the evidence just isn’t there to support this idea. “The well-done human studies have really never suggested this,” he said, and the studies that have were often performed on animals or cells (like breast cancer cells in a petri dish) and used “unbelievably toxic levels” of the ingredients they were testing.

Anyway, Dr. Burstein added, only a minuscule fraction of aluminum can be absorbed through the skin, so your exposure to it from an antiperspirant is trivial.

There’s also been concern derived from decades-old research that found that Alzheimer’s patients’ brains had high levels of aluminum. This suggested that the metal — perhaps not only from antiperspirants, but also from other personal care and household products like pots and pans — could be a potential risk factor for this degenerative disease. But scientists now disregard the idea that aluminum can cause Alzheimer’s. “The evidence is of poor quality, generally speaking,” said Amy Borenstein, a professor of epidemiology at the University of California, San Diego, who studies the causes of Alzheimer’s disease. “The whole topic has kind of been abandoned.”

She did note that the link between aluminum and Alzheimer’s is challenging to study because aluminum is the third most common element in the Earth’s crust, which means that everyone is exposed to it in small quantities.

“We believe it’s important for people to have choices to find the everyday products that are right for them,” said Justin Boudrow, a spokesman for Tom’s of Maine, which makes a variety of natural personal care products including toothpastes, mouthwashes, soaps and underarm products. “This is why we offer natural deodorants without aluminum that provide odor protection, as well as antiperspirants that do contain aluminum for wetness protection.”

Are natural deodorants good for your microbiome?

There isn’t enough evidence to show that they are. There have been claims that regular deodorants and antiperspirants can disrupt or kill off the “good” bacteria living in your armpits, leading to skin irritation, redness, bumps and overall poor skin health. Some natural deodorant brands have marketed their products as “microbiome friendly,” claiming that they’re not only good for the health of your skin, but also minimize odor by promoting the growth of “good” bacteria.

But Jack Gilbert, a skin microbiology expert at the University of California, San Diego, said that he wasn’t aware of any rigorous studies that have borne this out. “There’s a lot of associative work, but nothing that definitively links deodorant or antiperspirant disruption of the skin microbiome to skin health.”

Are the ingredients in natural deodorants better than those in traditional ones?

No. Just because a deodorant is labeled “natural” doesn’t mean it won’t contain any problematic ingredients itself. In fact, the term “natural” has no regulatory definition, so its labeling on personal care products is essentially meaningless.

“You can get irritation or allergic rashes, and that’s far and away the more common health issue seen with deodorants — all deodorants, whether traditional or natural,” said Dr. Jennifer Chen, a clinical associate professor of dermatology at Stanford Medicine. The most common issue with deodorant is irritant contact dermatitis, or skin irritation, Dr. Chen said, which “usually can’t be pinned down to a specific ingredient, even though some ingredients are more irritating than others.”

The most troublesome ingredient in any kind of deodorant or antiperspirant, whether it’s “natural” or not, is fragrance, said Dr. Nina Botto, an associate professor of dermatology at the University of California, San Francisco. This includes essential oils, which many natural deodorant brands play up in their marketing. “Botanicals, plant extracts and essential oils are often touted as having health benefits,” Dr. Botto said. “But those natural components actually cause a lot of health problems and trouble for the skin.”

The combination of the underarm’s thin, folding skin, hair follicles and moist environment makes this area of the body more susceptible to irritation or an allergic reaction compared to, say, if you put deodorant on your back. In fact, Dr. Chen noted, one study on fragrance allergies found that among many of the scented personal care products tested — like scented deodorants, lotions, shampoos, shaving creams and hair dyes — the deodorants caused the most cases of allergic contact dermatitis, a skin rash caused by contact with an allergen.

Dr. Botto said that while she still sees allergic reactions to synthetic fragrances, she’s been getting more and more patients who are dealing with allergic contact dermatitis after using products with natural fragrance, like those containing linalool and limonene — natural compounds extracted from certain plants, like citrus fruit peels, which are commonly used in natural deodorants.

Even worse, “a lot of times you’ll see that someone gets a rash with a natural deodorant and they’ll put on balms and other ‘natural’ remedies that contain more of the same ingredients,” Dr. Botto said. “It’s kind of like adding gasoline to a fire.” She noted that such rashes can also cause breaks in the skin, which can then lead to infection. “It can be a real mess,” she said.”

Does natural deodorant even work?

The experts said they weren’t aware of any studies that reliably looked into how well natural deodorants work. But the way they’re formulated can offer clues.

Because regular and natural deodorants don’t contain aluminum (which is what helps antiperspirants minimize sweating) they typically rely on ingredients like fragrances and baking soda to mask body odor. This means that natural deodorants generally should function as well as regular deodorants do in terms of keeping you fresh. However, while the experts were not aware of any rigorous, head-to-head studies comparing the efficacy of natural deodorants versus antiperspirants, it stands to reason that they may not counteract smell in the same way that an antiperspirant does. “Bacteria are stimulated to grow by the available water and nutrients found in sweat,” Dr. Gilbert said. “So antiperspirant is getting to the main route of the odor problem.”

Dr. Arielle Nagler, an assistant professor of dermatology at the N.Y.U. Grossman School of Medicine, said that the effectiveness of a product will also depend on how it interacts with your own biology. “Everyone smells a little bit different,” she said, which depends on how much you sweat and what kinds of bacteria are on your body.

Should I buy natural deodorant or not?

Natural deodorant is not better or worse for your health than traditional deodorant or antiperspirant. “A lot of the claims that one product is better than another are just marketing claims that are not based on scientific evidence,” Dr. Chen said. “I don’t think there’s any proof that one is safer than another.”

The Personal Care Products Council, an industry group that represents cosmetic and personal care product companies, echoed a view from Dr. Chen and other experts, which is that people should make their choice based on personal preference. “Our members work to ensure consumers have access to an array of safe and effective products that help meet the differing needs for themselves and their families,” the council said in a statement provided to The New York Times. “This includes offering ‘natural’ products for those consumers who prefer them. It’s all about consumer choice.”

Still, dermatologists do recommend fragrance-free options, especially if you are allergic or sensitive to fragrance. “The more exposure one has to some of these fragrance chemicals, the more at risk you are for potentially developing an allergy,” Dr. Botto said.

If you enjoy using scented deodorants, though, “that’s fine,” she added, “but particularly if you have any sort of skin sensitivity, it’s a risk.”

Or, you could simply choose not to wear deodorant at all.

Annie Sneed is a science journalist who has written for Scientific American, Wired, Public Radio International and Fast Company.

Julia Calderone contributed reporting.

Exercise May Ease Hot Flashes, Provided It’s Vigorous

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Hot flashes are a lamentable part of reaching middle age for many women. While drug treatments may provide relief, two new studies suggest that the right type of exercise might lessen both the frequency and discomfiting severity of hot flashes by changing how the body regulates its internal temperature.

As estrogen levels drop with the onset of menopause, many women become less adept, physiologically, at dealing with changes to internal and external temperatures. The result, famously, is the hot flash (also known as a hot flush), during which women can feel sudden, overwhelming heat and experience copious sweating, a problem that in some cases can linger for years.

Hormone replacement therapy can effectively combat hot flashes, and antidepressants may also help, though drug treatments have well-established side effects. Weight loss also may lessen hot flashes, but losing weight after menopause is difficult.

So researchers at Liverpool John Moores University in England and other institutions recently began to consider whether exercise might help.

Endurance exercise, after all, improves the body’s ability to regulate temperature, the scientists knew. Athletes, especially those in strenuous sports like distance running and cycling, start to sweat at a lower body temperature than out-of-shape people. Athletes’ blood vessels also carry more blood to the skin surface to release unwanted heat, even when they aren’t exercising.

If exercise had a similar effect on older, out-of-shape women’s internal thermostats, the scientists speculated, it might also lessen the number or the intensity of their hot flashes.

Previous studies examining exercise as a treatment for hot flashes had shown mixed results, the scientists knew. However, many of those experiments had been short term and involved walking or similarly light exercise, which might be too gentle to cause the physiological changes needed to reduce hot flashes.

So for the two new studies, one of which was published in the Journal of Physiology and the other in Menopause (using the same data to examine different aspects of exercise and hot flashes), the researchers decided to look at the effects of slightly more strenuous workouts.

They first recruited 21 menopausal women who did not currently exercise but did experience hot flashes. According to diaries each woman kept for a week at the start of the study, some women were having 100 or more of them each week.

The scientists also measured each woman’s general health, fitness, blood flow to the brain (which affects heat responses) and, most elaborately, ability to respond to heat stress. For that test, researchers fitted the women with suits that almost completely covered their bodies. The suits contained tubes that could be filled with water. By raising the temperature of the water, the scientists could induce hot flashes — which typically occur if an affected woman’s skin grows hot — and also track her body’s general ability to deal with heat stress.

Fourteen of the women then began an exercise program, while seven, who served as controls, did not. (This was a small pilot study, and the researchers allowed the women to choose whether to exercise or not.)

The sessions, all of them supervised by trainers, at first consisted of 30 minutes of moderate jogging or bicycling three times a week. Gradually, the workouts became longer and more intense, until by the end of four months the women were jogging or pedaling four or five times per week for 45 minutes at a pace that definitely caused them to pant and sweat.

They also, in the last of those 16 weeks, kept another diary of their hot flashes.

Then they returned to the lab to repeat the original tests.

The results showed that the exercisers, unsurprisingly, were considerably more aerobically fit now, while the control group’s fitness was unchanged.

More striking, the women who had exercised showed much better ability to regulate their body heat. When they wore the suit filled with warm water, they began to sweat a little earlier and more heavily than they had before, showing that their bodies could generally dissipate heat better.

But at the same time, during an actual hot flash induced by the hot suit, the exercisers perspired less and showed a lower rise in skin temperature than the control group. Their hot flashes were less intense than those of the women who had not worked out.

Probably best of all from the standpoint of the volunteers who had exercised, they turned out to have experienced far fewer hot flashes near the end of the experiment, according to their diaries, with the average frequency declining by more than 60 percent.

These findings strongly suggest that “improvements in fitness with a regular exercise program will have potential benefits on hot flushes,” said Helen Jones, a professor of exercise science at Liverpool John Moores University, who oversaw the new studies.

Precisely how exercise might change a women’s susceptibility to hot flashes is still not completely clear, although the researchers noted that the women who exercised developed better blood flow to the surface of their skin and to their brains during heat stress. That heightened blood flow most likely aided the operations of portions of the brain that regulate body temperature, Dr. Jones said.

The cautionary subtext of this study, though, is that to be effective against hot flashes, exercise probably needs to be sustained and somewhat strenuous, she said. “A leisurely walk for 30 minutes once a week is not going to have the required impact.”