Indoor humidity and your family's health

By Leanne Koster · 16 Feb 2016

Indoor humidity levels in the home can play an important role in family health, particularly where asthma and/or allergies are present. But do you know what the ideal levels are and how to achieve them? We’ve got the answers for you.

What is humidity?

Many people associate ‘humid’ with being sticky and uncomfortable on tropical holidays – an example of high outdoor humidity. But too high or low humidity can also affect us.

Relative humidity is a way of describing how much humidity (or water vapour) there is in the air, compared to how much there could be. When the temperature is warm, more water vapor can be in the air than when it is cold. 

What is healthy humidity?

Most people find that a relative humidity between 30 to 60 percent is the most comfortable, with indoor humidity ideally between 30 to 50 percent.

Low levels of humidity lead to very dry air which increases the prospect of catching airborne viruses like the flu, possibly due to both their ability to survive longer in dry cool conditions and irritated nasal passages making it easier to catch them. Eczema can be exacerbated and dry skin can also be uncomfortable.

Higher humidity in the home creates an environment for two of the most common and undesirable triggers for asthma and allergy – dust mites and mould.

Dust mites

Dust mites like moderate temperatures and high humidity (usually above 70 percent). They are found in bedding, flooring, window coverings and furniture. Their poo is the main culprit and is small enough to become airborne when stirred up.


Mould needs long periods of humidity to grow. Houses in tropical areas or with rising damp may be more at risk. Poor ventilation may mean a bathroom or built-in robe can produce mould, even if not in humid areas.

So how can I control the humidity in my home?

There are a number of ways that you can help control humidity levels in your home, depending on where you live and your climate.

  • Refrigerated air conditioners may reduce absolute humidity when they are cooling and relative humidity when they are heating.
  • Dehumidifiers will extract water from the air and reduce humidity.
  • Most forms of heating will lower relative humidity however it is a good idea to avoid unflued gas heating and open fireplaces.
  • Insulation helps keep your home warm in winter and cool in the summer.
  • Humidifiers may be suitable for very dry climates.
  • Except in very dry areas, an evaporative air-conditioner should not be used as it will increase humidity.
  • Ventilation and improved circulation of air can be a cheap and effective way of reducing humidity.
  • Heat recovery ventilation can also reduce relative humidity.
  • Extraction fans should be used in bathrooms and laundries as hot showers and dryers can dramatically increase relative humidity – these areas are often prone to mould growth.

Or it could be as simple as opening the window!

If you want to know the relative humidity in your home, a hygrometer will tell you. These are fairly cheap instruments; they are sometimes incorporated with thermometers or clocks.

More information

Check out our Indoor Humidity Factsheet for more great tips plus a handy graph showing the ideal temperature and humidity ranges for people with respiratory issues.

View our range of Sensitive Choice approved products and services that can help control your indoor environment, including heating, cooling, ventilation, purification, humidification and dehumidification.

Leanne K
National Asthma Council Australia

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