Humidity Doesn’t Just Make You Feel Gross. It Can Harm Your Health, Too

As summer approaches and temperatures begin to rise across the United States, it’s crucial to be aware of how the weather can affect your health as you plan your activities. While you probably know to be on alert for hot weather, another factor you may not think of but that is very important is humidity—which is a measure of the amount of water vapor in the air.

It might seem like having a little water in the air would be helpful on a sweltering summer day, but the meteorological reality is a little more complex than that. High humidity levels combined with elevated temperatures can create a dangerous mix, Kevin Lanza, PhD, assistant professor at UTHealth Houston School of Public Health, told Verywell.

“Humidity in and of itself is a lesser threat, at least at lower temperatures, but if you’re coupling that with higher temperatures, with hot and humid conditions that’s when you’re potentially in trouble,” said Lanza.

Here are the most important health effects of humidity that you should be aware of, and some expert-backed tips for coping this summer.

When Is Being Outside in Humidity Unsafe?

What’s considered an unsafe high humidity level varies depending on the individual, Shashank Ravi, MD, clinical assistant professor in emergency medicine at Stanford Medicine, told Verywell.

Specific factors, like your hydration level, how long you’re exposed to high humidity, and how much you exert yourself in these conditions, all play into how it affects your well-being. And it’s not just when you’re outside, either. “Being indoors in high humidity without circulating air can also be dangerous,” said Ravi.

In general, when humidity levels are high—above 60%–70%—it can make sweat evaporate from your skin more slowly. That, in turn, makes it harder for your body to cool itself, David Cutler, MD, a board-certified family medicine physician at Providence Saint John’s Health Center in Santa Monica, CA, told Verywell.

Inefficient sweating in high humidity “can make people feel hotter than the actual temperature,” said Cutler. “High humidity also increases the heat index, which is the perceived temperature. For example, an actual temperature of 90 degrees Fahrenheit can feel like 105 degrees Fahrenheit if the humidity is high.”

On the other hand, low humidity levels—below 30%–40%—can also negatively affect your health by causing dry skin and respiratory discomfort. “Low humidity can dry out mucous membranes in the nose and throat, leading to irritation, coughing, and increased susceptibility to respiratory infections,” said Cutler.

The best way to measure humidity levels is with a hygrometer, according to Cutler. The device, which may have a digital readout or dial like a thermometer, displays the humidity percentage relative to the maximum moisture capacity of the air at the present temperature. Basically, it shows you how much water is actually in the air relative to how much could possibly be held in the air at a specific temperature.

If you don’t have a hygrometer to get an exact reading, you can also check the humidity levels in weather apps or on forecast websites. Humidity levels also fluctuate throughout the day and will depend on other conditions, like rain.

How Does Humidity Affect Your Health? 

Humidity’s effect on the human body and your health really depends on how the level interacts with temperature, according to Lanza. While humidity by itself may not pose a major threat—especially at lower temperatures—its effects can be serious when combined with heat.

Our body’s thermal regulation system plays an important role in maintaining our internal core temperature, and sweating is the primary way we cool down, said Lanza. However, as mentioned before, humidity can really slow that process.

“That evaporation of the sweat from our skin is what cools the body and ultimately lowers our internal body temperature,” said Lanza. “But on days that are humid, sweating is not as effective at lowering the body’s internal temperature because the moisture in the air keeps the sweat from evaporating as easily.”

Therefore, high humidity can lead to health concerns and even make individuals “more susceptible to health risks like dehydration and fatigue,” added Ravi. Here are just a few things that can happen when you’re dealing with high humidity and heat:

• Dehydration: High humidity levels can lead to excessive sweating and cause the body to lose fluids faster, according to Ravi. If hydration levels are not replenished quickly, it can lead to dehydration and symptoms such as fatigue, dizziness, and confusion.
• Skin irritation: Humid conditions can cause skin irritation, such as heat rashes and even fungal infections, when there’s prolonged exposure to both heat and moisture, according to Lanza. High humidity can also make the skin oily and worsen conditions like acne, added Cutler.
• Muscle cramps: In humid conditions, people may lose too many electrolytes, which can shock the muscles and lead to cramping in the arms, legs, or abdomen, according to Lanza.
• Worsen respiratory conditions: High humidity can exacerbate respiratory conditions like asthma and allergies by promoting the growth of mold, dust mites, and bacteria, according to Cutler, who added that the thick, moist air can trigger breathing trouble and symptoms.
• Heat exhaustion and heat stroke: High humidity can increase the risk of serious heat-related illnesses such as heat exhaustion and heat stroke because the body’s cooling mechanism is less effective, according to Cutler. When the body can’t regulate its own temperature and starts to overheat, it can cause organ damage or even failure.

Who Is Most at Risk for Heat-Related Illness? 

Everyone is affected by extreme heat and humid conditions, but certain groups are more vulnerable to heat-related illness than others, according to Lanza.

• Young children: Children—especially infants and toddlers—have a smaller body mass to surface area ratio than adults, which makes them more susceptible to heat stress.
• Older adults: Older adults are at higher risk of heat-related illnesses and may even be more like to die from them due to age-related changes that make them less effective at regulating their body temperature. As we age, our bodies produce less sweat, affecting our ability to cool down in hot environments.
• Individuals with existing medical conditions or chronic conditions: People with chronic conditions such as cardiovascular disease, hypertension, and respiratory disorders are more vulnerable to extreme heat and related conditions because they can be less likely to sense and respond to changes in temperature. People who are overweight or obese may also retain more body heat, which can make overheating more likely.
• Those on certain medications: Diuretics, antihistamines, antidepressants, and other medications can interfere with the body’s ability to regulate temperature and increase the risk of dehydration.
• Individuals who work in outdoor conditions: People who work outdoors, such as construction workers, agricultural workers, and landscapers, are at a higher risk for heat illness due to prolonged exposure to high temperatures paired with physical exertion.

Early Signs Humidity Is Negatively Affecting Your Health 

It’s important to recognize the early signs that weather conditions like heat and humidity are affecting your health, according to Ravi. Some early indicators that humidity might be affecting your health are similar to symptoms of heat exhaustion or heat stroke, which include:

• Increased sweating
• Heart racing
• Weakness
• Fatigue 
• Difficulty walking
• Dizziness
• Headaches
• Nausea and vomiting
• Muscle cramps
• Fainting
• Confusion or altered mental status in severe cases
  

If you notice any of these early symptoms, Lanza recommends stopping physical activity, such as running or biking, or removing yourself from the situation that caused the symptoms—be it seeking shelter in the shade or going inside a climate-controlled, air-conditioned environment. You should also replenish lost fluids with cold water or a sports drink to restore electrolyte balance.

How to Stay Safe During the Summer 

With summer around the corner, your best defense is taking proactive measures to prevent heat-related illnesses and the health effects of high heat and humidity, according to Lanza.

“The best way to prevent symptoms is to never allow them to even start by being proactive with how one prepares in the warm season, especially from May to September in the United States,” Lanza said.

Here’s what you can do this summer season to avoid putting your health at risk in high temps and humid conditions:

• Check the weather and humidity levels before going outside: Lanza recommends checking the weather no matter what your plans are, but definitely if you’ll be doing outdoor activities. Knowing the forecast for heat and humidity can help you prep and pack accordingly, such as making sure you have enough water or sunscreen.
• Limit sun exposure/exercise during hotter times of day: Ravi suggests avoiding being outside during peak heat hours to reduce the risk of heat-related illness. If you plan to exercise, try to do so when it’s cooler, such as in the early morning hours or late evening, to avoid the risk of overheating or dehydration, Lanza added.
• Take breaks in cool or air-conditioned environments: When you can, take breaks and spend time in cool or air-conditioned environments to help lower your body temperature, said Lanza. If you don’t have air conditioning at home, head to places like local coffee shops, malls, libraries, museums, or community centers.
• Wear light-colored and loose-fitting clothing: Opt for light-colored, loose-fitting, and lightweight clothing to help your body stay cool, said Lanza. Flowy and lightweight clothes let air circulate against your skin, allowing sweat to evaporate instead of trapping it.
• Stay hydrated: It’s important to drink plenty of water throughout the day to maintain your level of hydration, Lanza said. Avoid drinks that contain alcohol or caffeine, as they can contribute to dehydration.
• Have your social network nearby: A lot of heat-related illnesses and medical emergencies occur because people are alone or don’t recognize their symptoms, according to Lanza. When you have social support nearby, you can have someone to help you in case of an emergency—or even simply remind you to rest and rehydrate.