How does humidity affect me?


by Geraldine Freeman, M.D.

Humidity is the amount of moisture in the air. Relative humidity is given as a percentage: the amount of moisture in the air relative to the greatest amount that air could hold. It can range from completely dry air, 0% relative humidity (say, in the Sahara Desert) to saturated air at 100% relative humidity (fog, a rainstorm, or a wet day in the tropics). Warm air can hold more moisture than cold air, so if you bring cold winter air into your house and warm it up, the relative humidity goes down. The air becomes effectively drier, and will draw moisture out of the surroundings – including the people in the house. The more you heat the air, the drier it behaves.

Extremely dry air is uncomfortable. It pulls water out of the skin, eyes, mouth, nose, and throat. A reasonable humidity level will provide more comfort. Humidity can be added to a home by way of small humidifiers, or a humidifier installed on a central heating unit. On the latter, there should be a humidistat to keep the moisture level at about 35%. Freestanding console humidifiers can increase the humidity of a whole house, while small humidifiers or “misters” can raise the level in a room. Sometimes a small humidifier, as in a child’s bedroom, will raise the humidity excessively, dampening the room and promoting the growth of mold and house dust mites. Avoid hot water humidifiers, which can be tipped over, sometimes burning children. Keep any humidifier meticulously clean and maintain it according to the manufacturer’s instructions, to prevent an unhealthy and dangerous growth of mold and bacteria.

A kettle of water on the kitchen stove or a wood stove does not introduce any significant humidity into the home.

In warmer weather, when an air conditioner is running, it raises the humidity, sometimes so much that excess water condenses and drips off of the unit. Adding moisture then is unnecessary, and will only make the air conditioner work harder. Evaporative coolers, of course, produce moist air which does not need any additional humidification.

Posted in: Home Environment

Allergy and the Environment