Humidity is a measure of the amount of water vapor in the air. Relative humidity measures the amount of water in the air in relation to the maximum amount of water vapor (moisture). The higher the temperature, the more water vapor the air can hold. Relative humidity is what your morning weather reporter would refer to.
Humidity is a natural part of our atmosphere, it comes from the amount of water vapor in the air. Water vapor enters the atmosphere by evaporating from the large bodies of water on the Earth’s surface including lakes, oceans, and seas.
It is an integral part of the water cycle, as water vapor is continuously generated by evaporation and removed by condensation. When the temperature is higher, the air can hold more water vapor, meaning that the warmer the climate, the higher the humidity level can be.
For example, a densely saturated amount of air may contain 28 grams of water per cubic meter at 30°C, but only 8 grams of water per cubic metre of air at 8 °C3.
Colder air cannot handle as much moisture as warmer air. Temperature in relation to humidity is important, especially as we spend 90% of our time indoors. Consider for example a winters day. The outdoor air could have a 100% relative humidity at 5°C, and therefore contain 6.8 grams of water. Indoors however, 5°C would be very uncomfortable, so we would warm it up. When the outdoor air is heated up to 23°C indoors, the absolute amount of water in the air is still the same. But since warmer air can hold more water, the relative humidity goes down to 33%.
On the other hand, warm air can handle more moisture than cooler air. For example, a warm and humid summer with 80% humidity at 30°C, would mean that the outdoor air contained 24 grams/m3 of water. In our homes, 30°C would be very uncomfortable so many would use air conditioners to cool it down again. If you cool it down to below 26°C, the relative humidity level goes to 100% and the water condenses (The dew point). That is why air conditioning systems often have a dehumidifier built-in. Without them, your walls in the home would be soaking wet during the summer.
A 100% relative humidity level would mean that the air is completely saturated with water vapor. Unable to hold any more, it would rain.
Colder climates often have lower humidity levels than warmer climates as colder air holds less moisture than warm air. In winter, humidity levels tend to be typically lower. Whereas in summer, humidity levels will be higher, as air can hold more water vapor at a higher temperature.
Small everyday tasks can affect humidity levels. Cooking, cleaning, dishwashing, breathing, clothes washing, showering, and other indoor processes release moisture into the indoor air, making indoor humidity levels rise.
Maintaining healthy humidity levels inside your house is vital. Poor humidity levels can have an impact on your health and the house itself. Too much humidity can cause dampness and mold, too little means the air becomes dry and uncomfortable.
21% of the 21.8 million cases of asthma annually are attributable to residential dampness and mold4. The humid conditions provide an excellent home for bacteria, as well as mold growth. The excess moisture in buildings can be caused by leaks, rain seeping in through windows and basements, or even rising damp from the ground floors.
Humidity levels above the recommended 50%, is when the air will start to feel dense and damp. More problems can develop as the levels rise.
Did you know that dust mites could not survive without humidity from the air?5 Dust mites like moderate temperatures and high humidity as they absorb water from it, so areas with high humidity levels are great places for them to live. The microscopic creatures can worsen allergies and asthma, so maintaining healthy humidity levels is key to minimizing them and their effects.6
Itching and dryness can be caused by low humidity. Studies have also found that low humidity should be avoided to protect the tear film in your eyes7. It can also aggravate certain skin conditions such as eczema8. Very dry air can extract moisture from the skin and make eczema worse9.
Measurable changes in your ability to concentrate or perform tasks can be caused by even small changes in the relative humidity and temperature.