High humidity makes us sweat in summer, and that makes hot weather feel so much more oppressive. But low humidity also can have adverse effects on your physical health and on your home environment. Knowing what low humidity is, and learning to identify the signs of low humidity, are important aspects of your family's health.
Humidity refers to the amount of water vapour in the air. When meteorologists measure the amount of water vapour in a specific volume of air, that measurement is called absolute humidity. Absolute humidity is also called specific humidity.
Relative humidity is a measurement of the humidity relative to the temperature. It is expressed as a ratio, or a percentage, that indicates how much water vapour is in a particular volume of air relative to the maximum amount of water vapour that particular volume of air can hold at that particular temperature. That maximum is called the saturation point.
Highs and Lows
At higher temperatures, the air can hold more water. When the relative humidity is high, it feels hotter outside, because there is more moisture in the air. When the relative humidity is low, it feels less hot at the same temperature because there is less moisture in the air.
In winter, high relative humidity makes cold temperatures feel even colder. That may seem counterintuitive, but it's the same principle. When it's cold, the air cannot hold as much water as it can at higher temperatures -- but when the relative humidity is at or near the saturation point for that temperature, it makes the same cold temperature feel even colder than it would if the relative humidity were lower.
Low Humidity and Your Health
The signs of high humidity are well known and include: excessive sweating, feeling hot and sticky, and the danger of heat stroke. However, low humidity can be equally problematic. Low relative humidity (defined as under 30 per cent) can cause or aggravate dry and cracked skin, sinus problems and chapped lips.
Low relative humidity in indoor environments, as well as the heat levels we maintain indoors in cold weather, dries out the mucous membranes that defend against colds and flu and other respiratory diseases. Dry nasal passages can also worsen symptoms of asthma.
The Best Defense
One of the best ways to defend against the adverse effects of cold, dry air is to use a humidifier. By increasing the moisture in the air, humidifiers can prevent or ease dry, cracked skin and provide relief for the symptoms of colds, flu and chronic respiratory conditions such as asthma.
The beneficial effects of humidifiers are best achieved through proper maintenance. If the humidifier is not kept clean, it can become a breeding ground for disease-causing bacteria and moulds that can actually cause illness and make allergies and respiratory conditions worse. It's also important to keep the humidity level in your home at a healthy level -- neither too high nor too low. According to the Mayo Clinic's website, the humidity level should not go below 30 per cent or above 50 per cent.
Some humidifiers come with a built-in "humidistat" that you can set to your preferred level. You can also purchase a hygrometer: a humidity "thermometer" that measures the humidity level in your home, just as a thermostat would measure the temperature.
- National Snow and Ice Data Center: Arctic Climatology and Meteorology
- National Science Digital Library:Glossary of Atmospheric Terms
- WashingtonPost.com: Weather Definitions and Explainers
- Health for World.com; Low Humidity Can Significantly Aggravate Signs of Asthma; Nov. 23, 2010
- Climate Effects on Human Health; Laurence S. Kalkstein, et al.; 19897
- The Mayo Clinic: Humidifiers - Air Moisture Eases Skin, Breathing Symptoms
- Jupiterimages/Creatas/Getty Images