Your body's ability to cool itself itself is severely compromised by sultry days. "You may feel more uncomfortable on a humid day because your body is not as easily able to evaporate the sweat on your skin, due to the moisture in the air," Christina L. Belitsky, M.S., RPA-C, a physician assistant with healthcare provider Northwell Health-GoHealth Urgent Care, tells Bustle. "Evaporation of sweat on our skin is our body’s way of naturally cooling us down in warm temperatures."

Hot and steamy days mean that sweat barely dries at all — and your body keeps getting hotter. This is why the air in humid climates can seem oppressively hot, while the same temperature in dry environments feels more acceptable.

This may be why hot, damp weather affects our mental health in ways that dry heat doesn't. An Australian study published in PLoS One in 2016 found that the more humid a hot environment was, the more likely people were to experience mental distress. Muggy weather can feel blissful up to a point, and then you feel like you're swimming in unbearable, choking heat.

Going outside and working up a sweat in an environment with lots of moisture in the air can be a real workout for your heart. "Not only does humidity make the temperature feel hotter than thermometers register, it makes our bodies work hard to stay cool," Dr. Seema Sarin M.D., director of lifestyle medicine at EHE Health, a healthcare provider, tells Bustle. Mugginess, she says, tends to increase blood circulation and breathing, as the body tries hard to decrease its core temperature and stay comfortable.

This, Dr. Nesheiwat explains, is why you might feel dizzy or nauseous in really steamy weather, particularly if you've been exercising. A study of distance runners published in Temperature in 2016 found that the higher the relative humidity, the more stressed their circulatory systems and hearts became as they ran.

While people with asthma know that breathing in cold, dry air can inflame their airways, it turns out that hot, wet air can do much the same thing. A study published in American Journal of Respiratory and Critical Care Medicine in 2012 found that breathing in humid air could cause airway constriction, but a dose of anti-asthmatic medication before exposure could help.

However, moist air can help as well. "Humidified air is a frequently used treatment for many things such as asthma, allergies, colds, even nasal congestion," Belitsky says. Putting a towel over your head as you inhale steam is an old-school way of clearing a head cold that actually works; the moisture loosens the mucus, making it easier to blow your nose.

Sweating constantly in steamy weather can be seriously uncomfortable (yay, sticking to seats), but it can also mean you get dehydrated. "When you sweat and perspire, you can lose electrolytes such as sodium and chloride, which the body needs to function," Dr. Nesheiwat says. "It's very important to stay hydrated to avoid fainting, muscle cramps, and overheating — especially in the summertime." Drink lots of water or drinks with electrolytes when the mercury peaks and humidity rises.

At its worst, high humidity can cause a condition known as heat stress, where your body stops being able to cool itself down at all. "Heat exhaustion occurs when your body temperature rises over 104° F," Dr. Sarin says. "You'll feel dizzy and dehydrated, and your heart may be racing."

A study published in 2020 in Environmental Research Letters suggests that by 2100, over 1 billion people will experience heat stress related to rising heat and humidity levels. Untreated, heat stress can turn into heat stroke, where you can experience serious damage to your internal organs — so anybody who's feeling really overheated needs to lower their body temperature with fans, cooling liquids, and a seat in a cold place.

Fortunately, most people will just feel better on a sticky day with some cold air. "Next time you feel uncomfortable on a humid day, turn a nearby fan on to get more comfortable," Belitsky says. "As always, for any concerning symptoms consult your doctor right away.”

Experts:

Christina Belitsky MS RPA-C

Dr. Janette Nesheiwat M.D.

Dr. Seema Sarin M.D.

Studies cited:

Che Muhamed, A. M., Atkins, K., Stannard, S. R., Mündel, T., & Thompson, M. W. (2016). The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat. Temperature (Austin, Tex.), 3(3), 455–464. https://doi.org/10.1080/23328940.2016.1182669

Ding, N., Berry, H.L., Bennett, C.M. (2016) The Importance of Humidity in the Relationship between Heat and Population Mental Health: Evidence from Australia. PLoS ONE 11(10): e0164190. https://doi.org/10.1371/journal.pone.0164190

Dixon, W.G., Beukenhorst, A.L., Yimer, B.B. et al. (2019) How the weather affects the pain of citizen scientists using a smartphone app. npj Digit. Med.2, 105. https://doi.org/10.1038/s41746-019-0180-3

Hayes, D., Jr, Collins, P. B., Khosravi, M., Lin, R. L., & Lee, L. Y. (2012). Bronchoconstriction triggered by breathing hot humid air in patients with asthma: role of cholinergic reflex. American journal of respiratory and critical care medicine, 185(11), 1190–1196. https://doi.org/10.1164/rccm.201201-0088OC

Li, D., Yuan, J., Kopp, R. (2020) Escalating global exposure to compound heat-humidity extremes with warming. Environmental Research Letters, 2020; DOI: 10.1088/1748-9326/ab7d04