It’s way too hot, not just in the United States, but in other parts of the world as well. The temperature in Rome this week was 107 degrees Fahrenheit. It is anticipated that the islands of Sicily and Sardinia could reach as high as 118. Temperatures were also dangerously high in Athens, leading authorities there to close the Acropolis. Many countries in Europe do not have air conditioning. Sanbao in China broke records at 126 degrees. In the Middle East, the heat index was over 150 degrees, which is not compatible with human life. Death Valley in the United States recorded a near record of 128 degrees. People in Florida can’t even cool off by getting into the ocean. Water temperatures there have been close to 100 degrees. Learn how such extreme heat challenges human health.

Last year, a summer heat wave killed more than 60,000 people in Europe. When temperatures rise, what are the dangers? You may also wonder who is most susceptible to the problems of excess heat. To find out, we talked with the interim director of the Center for Climate, Health and the Global Environment. Dr. Kari Nadeau points out that human bodies have difficulty dispersing excess heat when the ambient temperatures get warmer than our usual body temperatures.

Dr. Nadeau points out that older individuals, pregnant people and infants as well as those with chronic conditions have particular difficulties responding to high heat. In addition, many people with chronic conditions, especially hypertension, diabetes, asthma and cardiovascular disease, are likely to suffer ill effects from heat challenges. People who live in under-resourced communities are prone to these conditions and may also have difficulties finding a cool place to ride out the heat wave. One approach Dr. Nadeau suggests if you don’t have access to air conditioning is to set up a fan and have it blow air on you over a container of ice water.

When heat challenges our capacity to cope, the damages show up in stages. The mildest stage of heat stress can make people feel dizzy (heat syncope). They may notice mild swelling in the feet or fingers, and they may experience muscle cramps or a rash. Withdrawing from heat is usually adequate to address these problems.

At the next stage, termed heat exhaustion, people start to feel weak and nauseated. They often suffer with headaches and more severe dizziness or faintness. Their bodies may become depleted of salt (and possibly other minerals), and they may experience elevated body temperature and extreme fatigue. These people require cooling, and fast.

The most severe stage is heat stroke. As people begin to experience overwhelming heat, the brain starts to fail. In addition to feeling dizzy, people may become confused and stop thinking clearly. As a result, they may not take the necessary steps to get emergency medical treatment. In these heat challenges, cells lining the blood vessels and the gut begin to deteriorate. When sweating stops, core body temperature rises dangerously and heart rhythm changes. This is a medical emergency.

Certain medicines make it harder for our bodies to meet heat challenges. Diuretics such as hydrochlorothiazide or furosemide are popular drugs used to treat hypertension or heart failure. But because they encourage the body to get rid of excess fluids, people taking these medicines have less ability to cool themselves by sweating.

Some drugs that usually make us sweat more (such as the antidepressants bupropion or paroxetine) may make it harder to sweat in response to heat challenges. Most importantly, medications that interfere with the ability to sweat may really cause trouble for people exposed to high temperatures. Antihistamines such as diphenhydramine (Benadryl and also the PM in nighttime pain relievers) are notable for this. Some medicines used to treat mental illness also block sweating and become dangerous in heat. We think it makes sense to ask the prescriber and the pharmacist if your medicines could make you more vulnerable to heat.

Kari Nadeau, MD, PhD, is the Interim Director of the Center for Climate, Health, and the Global Environment, John Rock Professor of Climate and Population Studies, and Chair of the Department of Environmental Health at Harvard T.H. Chan School of Public Health.

Dr. Kari Nadeau, MD, PhD,

Scott Hall, PharmD, is the senior manager of Pharmacy Clinical Practice for the Mayo Clinic Health System in the Wisconsin region.

Scott Hall, PharmD, senior manager of Pharmacy Clinical Practice for the Mayo Clinic Health System

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