Everyone has heard of the problems associated with dry air in a room.

In this article, we’ll present current research findings regarding the most comfortable level of humidity and explain why negative health effects can be minimized by maintaining a relative humidity above 40% and below 60%. Deviations from these indicators in any direction can result not only in irritated eyes and airways, but also in serious health problems, poor work performance and sleep quality.

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Low humidity

The majority of the human body is composed of water and when the humidity in the air decreases, our skin begins to dry out, and the body as a whole becomes dehydrated. The mucous membranes dry up, begin to crack, and this makes it easier for various viruses and bacteria to invade the body.

The academic term for this outer layer of skin that provides protection against the invasion of microorganisms and allergens and also prevents excessive water loss is stratum corneum (SC).

Even short exposure to a 10% humidity environment for 3-6 hours can induce a difference in the moisture content of the stratum corneum. A higher prevalence of atopic dermatitis was found in American states with low humidity, low UV exposure, low outdoor temperature, and the use of indoor heating.

Besides that, humidity affects the transmission and survival of airborne viruses, bacteria, and fungi. For example, measles, influenza, herpes varicella and rubella viruses survive longer when exposed to a relative humidity below 50%.

The incidence of respiratory infections increases during the winter when people are exposed to long periods of low humidity indoors.  

Signs of the air being too dry in your home include:

  • Mucous membranes drying up i.e. chapped lips, sore throat, and irritated nasal passages.
  • Slight coughing.
  • Dry skin on the face and hands. Peeling or cracking of the skin on hands.
  • Hair and clothes made with synthetic materials electrify.
  • The tips of the leaves of indoor plants dry up.

High humidity

Under these conditions, a person’s well-being deteriorates and weakness sets in. Prolonged exposure to high humidity reduces immunity and combined with high temperatures it may lead to a heat stroke as the body can't cool itself. Notably, people with chronic cardiovascular diseases, hypertension, and atherosclerosis are particularly affected by such conditions.

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Most fungi require a relative humidity of over 75% in order to grow. Accordingly, actively growing fungal populations are usually an outdoor problem, while indoors they are limited to areas such as kitchens, bathrooms, and walls and window frames that are subject to frequent condensation due to a high local relative humidity rate.

Mites are the main cause of allergies to house dust. Laboratory studies have established that populations of the ordinary house dust mite, Dermatophagoides pteronyssinus, reach  their maximum size during exposure to up to 80% RH. Some studies claim that mite populations are almost entirely eliminated in winter when the relative humidity drops below 40-50%.

Signs of high humidity in your home include:

  • Heavy breathing, as in a bath or in a greenhouse.
  • Dampness and mold in unventilated areas and a musty odor.
  • Condensation on windows and glass doors

To measure humidity at home you can buy a hygrometer. You can also keep track of indoor and outdoor humidity with the Atmotube app which has a special feature called Comfort Zone. Based on your current temperature and humidity level, the app tells you whether your conditions are optimal for your health.