scorecardresearch Skip to main content

How to tell if you are dehydrated in the extreme heat

A new toolkit offers a detailed guide to how much water to drink and cost-effective ways to stay cool.

Extreme heat — generally defined as temperatures over 90 degrees — makes it harder for our bodies to cool themselves and triggers upticks in heat-related illness and mortality.Ross D. Franklin/Associated Press

Extreme heat — generally defined as temperatures over 90 degrees — makes it harder for our bodies to cool themselves and triggers upticks in heat-related illness and mortality. Here’s how to stay safe.

Stay alert

“The most important thing is awareness,” said Dr. Gaurab Basu, a primary care physician and co-director of the Center for Health Equity Education & Advocacy at Cambridge Health Alliance. “We have to have a mindset that hot weather can impact our health.”

Extreme heat is the leading cause of weather-related deaths in the United States, more than tornadoes, hurricanes, flooding, and cold winter weather, according to the National Weather Service. And, with climate change, Boston is expected to see longer and more intense heat waves. According to a 2022 study, if greenhouse gas emissions continue unabated, Boston will likely see 33 to 62 days of extreme heat by 2070, up from an average of 10 days during the 2000s.

In response, the Center for Climate, Health, and the Global Environment at Harvard’s T.H. Chan School of Public Health and Americares rolled out new toolkits for climate-related emergencies, including heat waves.


Basu has been using them with patients and colleagues.

“It is important to understand that communities of color and low-income communities are disproportionately impacted by heat,” said Basu.

The kits, available in English and Spanish, aim to narrow that gap by providing essential information to everyone.

Know when you’re dehydrated

Taking preventive measures to decrease the risk of a heat-related illness is critical, he said.

Stay hydrated; if your urine is dark, drink 2 to 3 glasses of water, according to the toolkit.

The Climate Resilience for Frontline Clinics Toolkit

Water can also help cool your body. When temperatures exceed 95 degrees Fahrenheit, fans do little, and our bodies have more trouble dispersing heat. Experts recommend taking baths, showers, or wetting your skin with a wet towel. Spraying yourself with water while using a fan is especially effective.


Another option is visiting one of Boston’s 15 cooling centers, which are open through Friday at 5 pm.

Be mindful of your diet. Avoid alcohol, sugary and caffeinated drinks, like coffee or tea, during extreme heat. The toolkit also recommends eating easy-to-digest foods, like salads and fruits.

Basu said that changing your routine under the extreme heat advisory is important. Don’t exert yourself outdoors, especially between 11 am and 6 pm, if you do not have to.

Avoid wearing dark clothes, and instead opt for loose and light-colored garments, said Basu. Experts also urge everyone to wear sunscreen, hats, and other protective gear.

Who is most at risk?

Although everyone can be impacted by heat-related illnesses, infants, people 65 or older, athletes, pregnant people, and individuals with chronic illnesses are at a greater risk than others, according to the CDC.

Hot weather can also irritate the lungs, putting people with asthma and COPD at greater risk.

Outdoor laborers are especially vulnerable, said Basu.

Chronic illnesses and medication

Many medications affect your body’s ability to deal with heat, including medicines for high blood pressure and SSRIs for depression and anxiety. If you take any of these, make sure to remain cool and well hydrated.

People with diabetes are also more prone to becoming dehydrated, making their blood sugar levels hard to control, and heat can damage equipment including test strips, insulin pumps and glucose monitors. The toolkit offers advice on how to keep equipment safe and stay hydrated throughout the heat wave.


Heat can also impact our mental health, said Basu, especially for individuals with chronic mental health conditions.

“If you’re part of this population of folks,” Basu said, “you really need to be staying in a place where you’re not going to be overheating because it could really impact your health.”

Nevertheless, experts recommend continuing to take medication as prescribed, unless indicated otherwise by your provider.

The difference between heat stroke and heat exhaustion

According to the Cleveland Clinic, heat exhaustion is less dangerous, but can come with muscle cramps, headaches, dizziness, weakness, fatigue, nausea, and vomiting.

Heat stroke is the most severe form of heat illness, with symptoms of confusion, altered mental status, and a very high core body temperature above 104 degrees Fahrenheit.

If you or anyone you know begins to experience heat stroke, call 911.

“Heat stroke is the most dramatic manifestation of the impact of heat on people’s health,” says Basu, “but I think we need to be aware of the more broad implications of heat on our health, and protect ourselves.”

Material from Globe wire services was included in this report.

Emma Obregón Dominguez can be reached at Follow her on Instagram @eobredom.