Reducing damp with a dehumidifier can help reduce allergies and asthma.

Dust mites thrive in damp conditions, and their faeces are known to be a leading asthma-causing allergen. Mould spores can also cause allergic reactions, and mould loves the damp.

Healthy homes

If you want to use a dehumidifier to help control moisture for health reasons:

  • Choose a model that has a high rate of water removal, and which allows you to set specific humidity levels using a display. This type is much more convenient when trying to set for low humidity levels.
  • Keep your house warm, as dehumidifiers work better when it's warmer, and the relative humidity drops as temperature rises.
  • Do everything you reasonably can to limit the amount of moisture in the air (see "Condensation control" below).

As for dust mites, the best way to reduce your exposure to them is to wrap bedding and mattresses in special covers, and vacuum regularly, using a vacuum cleaner with a HEPA filter.

Condensation control

  • Keep rooms ventilated and warm during winter - at least 7°C warmer than outside temperatures. Install heavy curtains and draw them at night: it helps keep the home warm and reduces the number of cool surfaces for water vapour to condense on. Leave windows closed on damp days.
  • Always use close fitting lids on pots when cooking and fit extractor fans over the cooktop or stove, and in the bathroom (these must be ducted to the outside).
  • Dehumidifiers have often been teamed with unflued LPG heaters. One spews out moisture (and other contaminants) while the second mops up the moisture. No, no, no. It’s not the dehumidifier that’s the problem here – it’s the unflued LPG heater. Their exposed flame is a fire risk and they fill the house with water and other harmful contaminants. Don’t use them. Use cheaper to run and safer electric heaters.
  • Use a cupboard heater in problem wardrobes. A ventilation grille in the top of the wardrobe will also help.
  • Vent clothes dryers to the outside and don't hang clothes inside to dry. Close doors when cooking, showering or using the dryer, to limit the spread of moist air.
  • Limit the number and size of pot plants in the house.
  • Check the ground under your house is dry. If it's wet, cover with polythene (if feasible), taping the joints, and ensuring a tight fit around piles. Check that drainage systems are diverting water away.
  • Fix any leaks in the roof or around windows.