Humid ‘hot spots’ pose health risks

Moisture is produced continuously within the home with the average family generating a staggering 20 litres of water per day.

Whilst this may sound harmless, excess moisture within the home can leave occupants vulnerable to a host of health risks.

Proffesor Awbi, indoor air specialist at Reading University explains,

“Excess moisture in the air can contribute to the presence of numerous airborne pollutants and create humid hot spots within the home”

“Moisture can affect the fabric of the building itself, degrading structural materials and leading to the release of potentially harmful chemicals. For example, formaldehyde is a pollutant released by numerous building materials such as plywood, carpets and textiles, and is water soluble – meaning its concentration increases as humidity rises”.

Formaldehyde can cause irritation of the eyes and upper respiratory tract, and the chemical is also a possible carcinogen at high concentrations.

Key contributors to polluted indoor air also include mould and dust mites, both of which thrive in moist, damp environments and are linked to exacerbations of asthma and allergies. Excess moisture may also promote bacterial growth and affect the survival of viruses.

Proffesor Awbi says:

“There is a worrying lack of importance placed on the quality of air in our homes.

“Indoor air can be many times more polluted than outdoor air with up to 900 possible pollutants, and excess moisture is a key contributor to the release of harmful compounds and toxins. As humans we breathe around 500 litres of air per hour and whilst we take care to eat and drink healthily, we also need to ensure the air we breathe is healthy”.

Effective ventilation is key to managing humidity levels and air quality within the home2, yet new survey results reveal that 45% of people do not even have an extractor fan in their bathroom, despite baths and showers adding up to a litre of moisture to the air in a day.

Proffesor Awbi comments:

“There needs to be increased awareness of this problem to prevent a rise in future health issues.

“We all need to think about improving ventilation in our homes and all new homes should have effective and sustained mechanical ventilation installed as standard. That’s why I am supportive of a ‘healthy home mark’ to ensure homes meet certain indoor air quality standards to protect our health.’’

More information on indoor air quality and health can be found at, together with details of the new Healthy Home Mark petition.


1. Bathroom

The average bath or shower creates 2 pints of excess water. This airborne moisture will settle on colder surface such as mirrors, taps, windows and walls and form condensation – which can lead to rotting wood, mould and the release of pollutants into the air. Simply leaving the door open won’t adequately address the issue and also allows the moisture to spread throughout your home. Keep the door closed and use an extractor fan to remove the moist air.

2. Kitchen

The kitchen has plenty of opportunities for moisture to build and settle. Cooking and boiling the kettle can add up to 6 pints of water to the air, and washing up can produce an extra 2 pints. To cut down on moisture production; wipe down wet surfaces, cook with lids on hobs, and keep the extractor fan on for about 20 minutes after you have finished in the kitchen, again with the door closed, to remove extra moisture.

3. Bedroom

Moisture is created even when you are fast asleep. One person adds as much as half a pint of water to the air overnight. As the warm, moist air leaves your body it rises – and then falls as it cools down. When this moist air descends it will settle on colder surfaces in the room such as walls or furniture. Without effective ventilation this can cause damp and mould to develop, in some cases this is mistaken for ‘rising damp’. The damp and mould can cause paint and wallpaper to peel and also produce spores and toxins which are harmful to health.

Ref: 84025