How Humidity Affects Our Health

If you get into a conversation about Houston summers, there's a good chance you'll hear the phrase, "It's not the heat, it's the humidity." And while the jury is out on the dry heat vs. humid heat debate, what's undeniably true is that humidity can affect our health, sometimes in surprising ways.

"High humidity can impair the body's ability to cool itself, leading to increased risk of heat-related illnesses such as heat exhaustion and heat stroke," says Dr. Sadeer Al-Kindi, a cardiologist-scientist and the medical director for the Center for Health & Nature at Houston Methodist. "It can also exacerbate respiratory conditions like asthma and allergies by promoting the growth of mold, dust mites, and other allergens.

Dr. Al-Kindi added that emerging literature suggests that high humidity, especially when combined with elevated ambient heat, is associated with increased cardiovascular risks, including a higher incidence of heart attacks, arrhythmias, and strokes. These effects may be driven by impaired thermoregulation, increased physiological strain and elevated core body temperature, all of which are captured more accurately by the heat index than temperature alone.

What is humidity?

Water can be either liquid, solid or gas. Water in its gas form is called water vapor — and humidity is the measure of water vapor in the air. While we often just say "humidity," there are two types: absolute and relative.

Absolute humidity is the actual amount of water vapor in the air. Relative humidity is a comparison measure of the current amount of water vapor in the air to the maximum amount of water vapor that could exist in the air at the current temperature. Written as a percent, it's what we think of when we hear "humidity" in weather reports — when relative humidity is 100%, the air is completely full of water vapor.

Dew point is another important measure to help us understand humidity. The dew point is the temperature the air needs to be cooled to in order to reach 100% relative humidity, which causes water vapor to turn into water droplets — rain, fog or dew on grass and windows. The higher the dew point, the more moisture there is in the air.

So how to judge our comfort outside from the weather report? Often, we think the relative humidity percentage is the key to understanding how muggy it will feel. However, it's actually the dew point that will tell you how humid it feels outside.

In general, the National Weather Service says that when the dew point is at or under 55 degrees, it feels dry and comfortable. Once the dew point is between 55 and 65 degrees, it can start to feel sticky, and evenings may feel muggy. Once the dew point is at or above 65 degrees, that's when humidity feels oppressive.

And we know something about oppressive, uncomfortable days here in Houston: our fair city has the highest dew point of any major Texas city, averaging 73.7 degrees during the three summer months.

So why does humidity feel bad?

Our bodies sweat to help regulate our internal temperature — but it's not the sweating itself that cools us down. It's when the sweat evaporates off the skin. When it's humid, there's so much moisture in the air that it prevents sweat from evaporating effectively. Your body doesn't cool, so you continue to sweat, and it collects on the skin, giving you that uncomfortable, damp, sticky feeling.

As time goes on, you can become dehydrated and show signs of heat exhaustion, including weakness, fainting and nausea. This can progress up to heat stroke if measures aren't taken to cool down.

"Heat illness can be life-threatening and often goes underappreciated, especially when humidity is high," Dr. Al-Kindi says. "When the body can no longer cool itself effectively, core temperature rises, placing immense stress on the heart and other vital organs. People should take hot and humid weather seriously, especially vulnerable populations such as the elderly, those with heart disease and outdoor workers."

3 surprising ways humidity affects our health

Humidity isn't just a factor in heat-related illnesses — it can also cause issues for people with other conditions.

1. It can make it harder to breathe

High humidity can cause bronchial constriction, which is when the airways narrow. Humidity can make it harder for all of us to breathe, but it can particularly aggravate symptoms in people with respiratory illnesses such as chronic obstructive pulmonary disease (COPD), allergies and asthma.

Plus, humidity creates ideal conditions for allergens to grow and thrive. Humid air can keep pollen and other irritants around much longer than in dry conditions, and the sticky environment can make it much easier for mold and bacteria to grow.

Folks with asthma or allergies may notice their symptoms become more serious when it's muggy outside.

"Humidity does not just make the air feel heavy," Dr. Al-Kindi says. "It also worsens air quality in ways that can significantly impact health. High humidity creates an environment where allergens such as mold, dust mites, and pollen can thrive, which may aggravate asthma and other respiratory conditions. For people with underlying lung disease or cardiovascular issues, breathing in humid and allergen-rich air can trigger symptoms and lead to serious complications."

2. It can affect your heart

Hot and humid weather can be a significant stressor on the heart. Heat makes blood thinner, which in turn makes the heart pump faster and stronger to try to keep the body cool. On a humid day, your heart may work two to four times harder, which can put people at risk for heart arrhythmia or a heart attack.

If you have high blood pressure or a history of heart disease, you'll want to take extra precautions in the heat, especially since certain medications can make you more vulnerable to heat.

RELATED: How Heat Impacts Your Heart Health

"Hot and humid weather places extra strain on the cardiovascular system," Dr. Al-Kindi says. "When it's humid, the body struggles to cool itself, forcing the heart to work harder to maintain a safe core temperature.

"This increased workload can lead to elevated heart rate and blood pressure, and in vulnerable individuals, it may trigger arrhythmias, chest pain or even heart attacks. People with hypertension or a history of heart disease should be especially cautious, as heat and humidity can interact with medications and increase the risk of complications."

3. It can affect your mental health

People often think of winter, with its cold temperatures and dark days, as the season that affects our mental health the most. But summer, with its heat, humidity and hurricanes, can affect our moods just as much. In a 2022 study, relative humidity was found to be the only meteorological factor that might affect depression symptoms.

In fact, increased humidity and temperatures have been associated with increased levels of stress, anxiety and even suicide rates. Humid weather can cause irritability, trouble concentrating and decreased motivation.

And, yes, you can have seasonal affective disorder (SAD) in the summer. The National Institute of Mental Health says that while summer-pattern SAD, or summer depression, is less common than winter-pattern SAD, it's a real condition. Summer-pattern SAD can have additional symptoms, including trouble sleeping, poor appetite, restlessness, agitation, anxiety, and even violent and aggressive behavior.

"While we often associate seasonal mood changes with winter, hot and humid weather can also take a toll on mental health" Dr. Al-Kindi says. "High humidity has been linked to increased levels of stress, anxiety, irritability, and depressive symptoms. It can disrupt sleep, reduce motivation and make it harder to concentrate.

"Humid conditions also limit opportunities for outdoor exercise, which is an important outlet for mental well-being. Interestingly, a study in mice showed that hot and humid environments may contribute to anxiety-related disorders by altering the gut microbiome, highlighting the complex ways in which environmental factors can influence mental health."

How to stay healthy during humid weather

Unfortunately, humidity is a constant companion for us here on the Gulf Coast. While we can't avoid it, we can take precautions that can help us lessen the effects of humidity on our health.

1. Check the weather, and be open to changing your plans

Did you open your favorite weather app and see it's going to be a scorcher? Consider rescheduling any physical activity to the coolest times of the day, either in the morning or early evening.

2. Stay hydrated and avoid alcohol

It's important to drink water (even if you don't feel thirsty) when you're in hot and humid weather because it's easy to become dehydrated when you sweat too much. Coffee and other caffeinated beverages can cause you to lose water quickly, so you may want to reconsider your iced coffee. And that espresso martini is a no-go in the heat as well — alcohol should be avoided.

3. Dress for the weather

If you can, dress in lightweight clothing made from breathable fabrics. Tight clothing can cause sweat to pool on your skin, which can lead to increased sweating.

4. Wear SPF and stay in the shade

If you have to be outside, make sure to wear sunscreen and try to stay in the shade. The heat index, or the "feels like" temperature you see in weather forecasts, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. It's calculated by the temperature in the shade, not the full sun. You can experience temperatures that feel up to 15 degrees hotter in direct sunlight, so it's safer in the shade.

RELATED: How Often Should You Reapply Sunscreen?

5. Stay in air-conditioned environments

While it's not as romantic as being next to a roaring fireplace in the winter, sitting near an air conditioner vent can be just as comfortable when temperatures are soaring. It's better to take it easy and stay inside where it's cool, especially if you're sensitive to heat due to age or a health condition.

If you don't have AC, open your windows and place cold water in front of a fan to circulate cooler air. Or during the hottest part of the day, go to air-conditioned places like the library, the movies or a local mall.