How High Relative Humidity Impacts Your Body (& Why It Feels More Miserable Than Dry Heat)

In the simplest terms, humidity is a natural occurrence of water vapor in the air. It plays a big part in how clouds are made, so it stands to reason that humidity affects the weather. However, it does more than that: It has an impact on your body as well. First, it's important to understand the difference between absolute and relative humidity. While absolute humidity is purely a measurement of moisture in the air, relative humidity is the measurement of moisture compared to the amount that can exist at the air's current temperature. Since warm air can contain more water vapor than cold air, you can begin to understand how high relative humidity can affect your body.

When your body temperature rises, its natural reaction is to sweat. Dry air helps your body cool down by evaporating the sweat off your skin. However, humid air makes it more difficult for that sweat to evaporate, which makes it harder for your body to cool down. As a result, you're more likely to feel miserable in humid heat than dry heat.

A series of health issues can develop like a domino effect when your body can't cool down because of high relative humidity. For starters, your body could respond by sweating excessively. That may lead to dehydration that can cause fatigue, muscle cramps, and dizziness, among other conditions. Your skin could even break out into a heat rash as the sweat on your skin lingers and inflames your sweat ducts. If your body remains too hot for a prolonged period, you could experience heat exhaustion, or worse, heat stroke, which is a life-threatening illness.

Aside from preventing your body from cooling down and the potential health issues that can develop from that, high relative humidity can affect your body in other ways. The simple fact that humid air contains more moisture than dry air has an impact on your ability to breathe. It means that the air is more populated with hydrogen molecules, so your lungs must work harder to get the reduced amount of oxygen per unit volume.

Additionally, high relative humidity goes hand in hand with poor air quality because it prevents airborne pollutants from dispersing as they usually would. When this happens indoors, you're more likely to breathe in those pollutants, which can trigger respiratory diseases and allergies, as well as aggravate existing health issues, such as asthma and chronic obstructive pulmonary disease. There's even a risk for infections to develop (via International Journal of Molecular Sciences).

Fortunately, a hygrometer measures the air's relative humidity so that you can monitor the levels and protect your overall health. When the levels are high outdoors, it's important to stay hydrated, wear breathable clothing, and take breaks from activity more often than you would in drier conditions. Indoors, you can use a dehumidifier to reduce humidity levels when they rise beyond 50%.