The air that we breathe is made up of numerous gases, including water vapor. The term humidity generally refers to the amount of this water vapor in the atmosphere. Each atmospheric gas has its own vapor pressure, a measure of the number of molecules present at a given temperature.
The vapor pressure of water thus measures the amount of water vapor in the air. The saturation vapor pressure is the vapor pressure when liquid water begins to condense. Relative humidity is determined by using the actual vapor pressure divided by the saturation vapor pressure see below. Meteorologists also use dewpoint temperature as a measure of the amount of water vapor in the atmosphere. This is the temperature at which the atmosphere becomes saturated and dew starts to form.
It is also defined as the temperature at which the vapor pressure equals the saturation vapor pressure. Thus, as the temperature approaches and equals the dewpoint temperature, the vapor pressure and the saturation vapor pressure become the same. When this occurs, dew starts to form.
This phenomenon is illustrated by a glass of cool iced tea on a warm muggy day. The air around the glass cools and water condenses on the outside of the glass. Human body temperature is dependent on the air as it absorbs and removes moisture from our skin to cool us down. If the relative humidity is high, the amount of water evaporating from our skin is limited so we feel warm and stifled. High and low levels of relative humidity within the home can have adverse effects for the occupants as well as the dwelling itself.
Hygiene, health, retention of value, aesthetics, and comfort are all areas which can be affected by a failure to maintain an optimal level of relative humidity. We've got an article on why humidity is so uncomfortable. According to a study in the journal Temperature , even highly trained athletes can struggle to perform in the heat, with high relative humidity creating "thermoregulatory and circulatory stress".
In the study, scientists demonstrate how high heat causes dehydration due to increased sweating, plus fatigue, muscle cramps and heat exhaustion.
The reason? Sweat struggles to evaporate in a humid environment, your body struggles to regulate its temperature, causing it to heat up. Even if it isn't hot, humidity can cause problems in the home.
Dust mites thrive in humid homes and often cause irritation according to the Mayo Clinic , including a stuffy nose, itchy eyes or skin, or wheezing and sneezing. High relative humidity is ideal for these invisible irritants to proliferate, scientists at the Asthma and Allergy Foundation of America have warned.
In a small-scale study published in in The Journal of Allergy and Clinical Immunology , researchers found that people who actively controlled the relative humidity in their homes using a high-efficiency dehumidifier or by simply leaving the windows open had dramatically lower levels of dust mite infection. While simply opening windows can help, a dehumidifier is also a practical solution to issues of humidity. Lawrie is a journalist and editor who writes about healthcare, science, technology, engineering and design.
There are several ways moisture can enter—and stay—in your home. Rooms where water is used frequently, such as the bathroom and kitchen, tend to be more humid than other areas of your home. Humidity can occur in your home due to:. This, of course, depends on the climate you live in, as well as your personal preference.
As temperatures rise and fall, the ability of air to hold water changes. When air is warmer, it can hold more water. When air is cooler, it cannot contain as much moisture. Excess relative humidity can cause poor indoor air quality which can harm your physical health and the health of your home, alike. If you live in a dry, desert climate, you may not deal with problems of relative humidity. However, other climates can leave your home in need of maintenance due to high levels of humidity.
Some home damage to watch out for when there is excess humidity include:. Poor air quality in your home due to high levels of relative humidity can do more than cause mold growth and peeling wallpaper—it may have a significant impact on your health. People with asthma, allergies, or otherwise compromised immune systems are likely to experience more problems. Still, people who have no underlying health issues may find that high humidity may cause physical ailments, too.
Since mold, mildew, and mites thrive in humid environments, they can trigger many of these symptoms. Some of the health effects from excess humidity may include:. While excessively high levels of relative humidity are known to be harmful, the same is true when levels are too low. However, the symptoms—both in your home and your body—of low levels of relative humidity are more obscure, so you may not notice them as readily.
When the air is colder outside , you probably use your heater or fireplace more. This can cause the humidity in your home to drop below ideal levels and cause the air to become excessively dry. Some of the ways low relative humidity affect your home include:.
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