Humidifiers & ionisers

Humidifiers and ionisers work in different ways but can help make the air better for asthma sufferers and therefore help reduce the symptoms that may bring on an asthma attack.


Humidifiers will raise the humidity of a room by adding moisture to the air and therefore children and adults with asthma will often find that a humidifier will help their breathing since it eliminates the dry air that can irritate and inflame the passages in the nose and throat.

Indoor humidity levels should remain between 40 and 60%. If the humidity level drops below 30% people can suffer from dry mucus membranes in their mouth which can lead to or aggravate the symptoms of asthma. Levels can be monitored with a device called a hygrometer, and many humidifiers will have these built in. Humidifiers tend to be more beneficial during the winter, when humidity levels are low and heating systems are in use since they dry the air out.

It is recommended that asthma sufferers use filter humidifiers that use a HEPA filter. These units will remove harmful toxins and allergens from the air and do not produce ozone. There are two types of humidifier:

  • Hot mist - these contain a heating element that boils water and then puts moisture into the air by sending out a stream of hot mist.
  • Cool mist - these force the water droplets into a mist by a mechanical action and then disperse the mist into the air. Cool mist is generally easier to breathe.

Any humidifier will need to be drained and cleaned frequently since bacteria can multiply in dirty and stale water. If the humidifier is being used for a child, it is better to use a cool mist humidifier to avoid accidental steam burns.

It is important not to keep humidity levels too high since this can make things worse by prompting the growth of mould or mildew.


Ionisers or negative ion generators, work by creating a static charge around the airborne contaminants that are floating around a room. Once charged with static, these particles (dust, allergens, pet dander etc.) simply stick to the nearest surface they find. The air feels fresh because the contaminants are no longer floating around in mid-air, but the fact is those contaminants are now firmly stuck to many of the surfaces of the room such as the walls, furniture, carpets and table tops. Therefore, you often see a ring of black around the base of an ioniser when it has been moved.

Some ionisers have “collection” plates inside them. These are supposed to collect the charged particles for you to wash off when the plates get full but, most of the particles have already stuck to the nearest surface in the room and very few actually make it all the way back to the ioniser.

Ultimately an ioniser air filter does not remove any of the offending particles from the room it simply deposits them onto a nearby surface. If you are seriously looking to improve the air quality in your home, you should be looking to remove the offending allergens and dust particles as opposed to just moving them around.

Sources used in writing this article are available on request

Information contained in this Articles page has been written by talkmusic based on available medical evidence. Our evidence-based articles are certified by the Information Standard and our sources are available on request. The content is not, though, written by medical professionals and should never be considered a substitute for medical advice. You should always seek medical advice before changing your treatment routine. talkmusic does not endorse any specific products, brands, or treatments.

Information written by the talkmusic team

Last revised: 18 March 2018

Next review: 18 March 2021

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