We in the Upper Midwest are no strangers to extremes in the forecast. From frigid winters to hot, humid summers, we contend with a wide range of temperatures throughout the year. It means we get to enjoy the full extent of what each season has to offer, but doing so requires knowledge of how to stay safe in any weather.

The dangers of cold weather, like hypothermia and frostbite, are familiar to us Minnesotans, but there are just as many risks in muggy weather.

Below, we’ll discuss how humidity affects our bodies with help from Marny Benjamin, MD, an emergency medicine doctor at Methodist Hospital. We’ll also give you some tips on avoiding the dangerous side effects of humidity on sweltering summer days.

What is humidity?

There’s usually no mistaking humidity. The air can feel like it is pressing against your skin, and you might find it more difficult to move and breathe. Humidity measures the amount of water vapor, or water in the form of gas, in the air. A high level of humidity means there is a lot of water vapor in the air.

In humid conditions, the air becomes populated by hydrogen and nitrogen as well as oxygen, and our lungs have to work harder to get oxygen from the air. This is part of the reason why we feel so lethargic in humidity, and why physical activity can be especially taxing.

High humidity can alter air quality

Unfortunately, humidity and poor air quality often go hand-in-hand. With so much water vapor in the air during times of high humidity, airborne pollution particles can’t disperse into the atmosphere as easily as they normally would. Humidity holds these particles close to the ground, increasing and sustaining the levels of air pollution around us.

The dewpoint determines how humidity feels

The National Weather Service (NWS) considers the dewpoint – the temperature the air must reach to be saturated with water vapor – the most accurate measure of how humid it feels outside.

While everyone has different comfort levels when it comes to conditions in the outdoors, the NWS generally considers a dewpoint temperature of 55°F and below to be comfortable. It’s when the dewpoint temperature climbs above 60-70°F that the air can become heavy, oppressive and uncomfortable, and your skin starts to get that sticky feeling.

High humidity makes it feel hotter outside

A forecast of 95°F is rarely the whole story once humidity begins to rise. According to the National Weather Service heat index, 95°F can feel like 107°F with just 50% humidity. The key word here is feel. In high humidity, the temperature isn’t actually hotter, but it feels that way to us because our bodies can’t cool down. So, what prevents our bodies from keeping cool in humidity?

We sweat in hot temperatures, and the action of sweat droplets evaporating off our skin cools us down. As Dr. Benjamin explains, “Sweat is one of the main ways the body cools itself. But on a humid day, sweat has a harder time evaporating into the air.” In high humidity, the air is already nearly full of water vapor and can’t hold any more.

“That’s where the hot, sticky feeling comes from. Sweat rests on our skin, unable to evaporate into the air,” Dr. Benjamin says. “As a result, our bodies continue to sweat and sweat – but feel no relief. Ultimately, high humidity throws the body into overdrive to cool itself. And with all that extra work, body temperature can rise.”

Most people agree that a hot day becomes increasingly unbearable when it’s humid out, and suddenly sunburn becomes just one of many things to worry about. This is because high humidity can make you sick in the form of heat-related illnesses.

“The inability to cool down leaves us more than just uncomfortable. It actually wears on our internal processes,” says Dr. Benjamin. “As our core temperature continues to rise, our bodies need to work harder to try and cool us down. This causes us to overheat.”

To stop us from overheating, the brain leaps into action, sending more blood to the skin where heat can escape (this is why warmth makes us flush) and widening blood vessels to increase sweating.

“This can lead our bodies to dehydration – losing the water, salt and chemicals that they need to function,” Dr. Benjamin says. And the diverted blood flow denies our other organs their normal blood supply. To make matters worse, these physical responses don’t work as well in humid conditions.

When our body is going haywire, we become vulnerable to a host of heat and humidity-related side effects like fatigue, muscle cramps and breathing difficulties. But it can also lead to more serious conditions, like:

  • Dehydration: As Dr. Benjamin said above, the excess sweating in extreme heat and humidity causes our bodies to lose essential fluids faster than we can replace them by drinking water. Feeling thirsty is the first sign that you’re becoming dehydrated. If you’re still not getting enough water, you’ll start sweating and urinating less, and could experience headache, stomach cramps and muscle spasms.
  • Fainting: When you faint in hot weather, it’s because the blood pressure in your brain has dropped as blood rushes to other areas of your body to combat the heat.
  • Heat rash: Excessive sweating can lead to heat rash when sweat becomes trapped under the skin. The rash area will have raised bumps that might feel itchy and sting.
  • Heat exhaustion: The sustained loss of fluids through excessive sweating can lead to heat exhaustion. If you feel weak, nauseous or dizzy after spending time in the heat, you are likely suffering from heat exhaustion. Left unaddressed, heat exhaustion can become heat stroke.
  • Heat stroke (hyperthermia): Heat stroke occurs when the body overheats, reaching internal temperatures of 104°F and higher. Someone suffering from heat stroke may suddenly stop sweating, have poor balance, become disoriented and confused, and lose consciousness. Heat stroke requires immediate medical attention.

High humidity can also aggravate existing health conditions

Certain health conditions make you more susceptible to the negative health effects of heat and humidity, and may cause you to have a more severe physical reaction. And the types of medication you take can also raise your health risk during the warmer months. The following conditions can be exacerbated by humidity and, at the same time, increase your chances of suffering a heat-related illness:

  • Asthma: When you have asthma, your lungs are more sensitive to multiple factors, one of which can be humidity. High levels of moisture in the air can trigger bronchoconstriction, or the narrowing of airways, in people with asthma. This leads to a flare-up in asthma symptoms, like coughing, wheezing and shortness of breath.
  • COPD (chronic obstructive pulmonary disease): Everyone has to work a little harder to breathe when it’s humid outside because the air is thicker. In someone with COPD, this breathing difficulty is magnified.
  • Heart disease and high blood pressure: Your heart needs to pump significantly more blood on hot and humid days just to keep you cool. This puts a lot of strain on your heart and circulatory system. If you have heart disease or high blood pressure, your heart may not be able to keep up, potentially leading to incidences of heart arrythmia, heart attack and heart failure.
  • Chronic kidney disease: Continuous sweating in the heat requires a lot of effort from the kidneys as they help manage blood pressure and the supply of water and electrolytes to the rest of the body. Chronic kidney disease can disturb these processes.
  • Diabetes: Your nerves and blood vessels can be damaged by diabetes, making it harder for you to know when you’re too hot and cool down effectively when you are. Diabetes can also cause more rapid dehydration in hot, humid weather. Plus, high temperatures speed up the body’s metabolism, which in turn leads to faster insulin absorption.
  • Allergies: Humidity creates ideal conditions for mold growth, and humid air holds in pollen and other irritants. If you have allergies, you may notice your symptoms become more severe on humid days or in indoor spaces with high humidity.

Ways to stay safe in high humidity

Summers in the Midwest tend to be pretty humid, but that doesn’t mean we can’t enjoy them. Below are a few tips for how to get the most out of the summer season without putting your health at risk:

  • Check the humidity level before venturing outside: Whatever your plans for the day, it’s always a good idea to check the weather beforehand, especially if you’re planning outdoor activities. Awareness of the forecasted heat and humidity allows you to pack enough water and sunscreen, and plan for the proper number of breaks in the shade.
  • Stay hydrated: The best way to stay on top of your hydration is to drink fluids before you get thirsty. You can pair your drink with a salty snack or choose energy drinks with sodium, as sodium helps your body retain the water you drink.
  • Consider easing up on strenuous outdoor activities: If you had planned for a long run, a hilly bike ride or a challenging hike on a humid day, consider shortening your distance, or reschedule exercise altogether (aside from swimming). Waiting for a cooler day with lower humidity will protect your health, and you’ll be more likely to actually enjoy your activity, rather than just endure it.
  • Pick clothing that breathes: Humid days are not the time to break out that tight dress you’ve been eyeing since winter. Opt for clothing with a looser fit, made from breathable fabrics like cotton and linen. Flowy clothes allow air to circulate against your skin and evaporate sweat rather than trap it. And choose cotton or linen sheets for cooler, more comfortable sleep.
  • Take a break in air conditioning: After sweating in the heat, even just a few hours in cool air can help your body recover. If you don’t have air conditioning at home, you can get some relief at your local coffee shop, movie theater, public library, museum or mall.

How to adjust to high humidity

The most important thing to do when adjusting to high humidity is to give yourself time. It takes about two weeks to adjust to a new climate. Don’t try to rush into all your regular activities without first allowing your body to acclimate in its own time.

You can increase the amount of time you spend in humid conditions a little more each day, just make sure to listen to your body.

How to monitor and control indoor humidity levels

The humidity levels inside your home should stay between 30-50%. Too much indoor humidity can affect your health in all the ways listed above and damage your possessions. It can even encourage the growth of mold and fungus. Too little humidity in your home and you could be dealing with dry skin and hair, frequent colds and coughs, and a breeding ground for viruses and germs.

To monitor the humidity levels at home, you can use a hygrometer, a device that measures the amount of moisture in the surrounding air. It looks very similar to a thermometer and can be purchased at hardware stores or online.

If it’s too humid at home, Dr. Benjamin recommends trying a home dehumidifier. “These are built to remove moisture from the air,” she says. And if the air in your home is too dry, a humidifier can put some of that moisture right back.

Feeling sick from heat and humidity?

It’s important to recognize when you or others are feeling more than just uncomfortable in hot and humid conditions. Don’t feel like you have to tough it out! Taking quick action to hydrate and remove yourself or someone else from the heat can prevent potentially dangerous situations.

If you or someone else is feeling unwell after spending time in the heat, our urgent care services are here to help. However, if you suspect heat stroke, call 911 immediately.