Humidity refers to the amount of water vapor, the gaseous form of water, present in the air. This invisible moisture plays a significant role in how comfortable conditions feel outdoors and can influence overall health. Understanding outdoor humidity levels is important for daily planning and well-being.
Gauging Outdoor Humidity
Outdoor humidity is typically measured and reported as relative humidity. This percentage indicates how much water vapor is currently in the air compared to the maximum it could hold at a specific temperature. Warmer air holds more moisture than colder air, meaning a high relative humidity on a cold day might contain less actual moisture than a lower relative humidity on a hot day.
Weather forecasts and smartphone applications commonly provide relative humidity readings, often alongside a “feels like” temperature or heat index. Hygrometers are used to measure this moisture content.
The Comfortable Range
A comfortable outdoor relative humidity level for most people falls between 30% and 60%. Within this range, the air contains enough moisture to prevent excessive dryness without feeling overly damp or sticky. This allows the body’s natural cooling mechanism, sweating, to work efficiently through evaporation.
Comfort also depends on temperature; lower humidity levels are more tolerable in hotter conditions, while higher humidity feels agreeable in cooler temperatures. The “heat index” combines air temperature and relative humidity to provide a more accurate measure of how hot it feels to the human body.
When Humidity is Too High or Too Low
When outdoor humidity levels climb above 60%, the air becomes saturated with moisture, making it difficult for sweat to evaporate from the skin. This leads to a sticky sensation and can cause the body to feel hotter than the actual air temperature, increasing the risk of heat-related illnesses like heat exhaustion. High humidity can also make breathing more challenging, especially for individuals with respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD), and can put extra strain on the heart. Consistently high moisture levels can promote the growth of allergens like mold and dust mites, and can trap pollen, potentially worsening allergy symptoms.
Conversely, when relative humidity drops below 30%, the air is very dry, pulling moisture from the body. This can lead to dry and itchy skin, chapped lips, dry eyes, and irritated nasal passages and throat. Low humidity also contributes to increased susceptibility to respiratory infections, as dry mucous membranes offer less protection against viruses and bacteria. A common effect of low humidity, particularly below 40%, is increased static electricity, as the lack of moisture prevents static charges from dissipating easily, leading to shocks.