Although the European Federation of Allergy and Airways Diseases Patients' Associations (EFA) estimates we spend up to 90 percent of our time indoors, levels of air pollutants inside homes and workplaces may be up to 10 times higher than outdoors.
Such pollution is caused by many things, including chemicals used for cleaning or decorating, heating, cooking, building materials, tobacco smoke, house dust mites and pet dander. And it can be exacerbated by poor ventilation, room temperature, damp, condensation, and pollution that has come indoors from outside.
Indoor air quality is crucial for human health, and particularly important for vulnerable groups, such as babies, children and the elderly, as well as people living with respiratory and allergic diseases.
Dr Nick Hopkinson, medical director at the British Lung Foundation, says: "Everyone knows outdoor air pollution poses a serious risk to health, but people often overlook the impact of air quality within our own homes. Smoking and any other source of smoke, as well as fumes from chemicals used for cleaning, can contribute to lung disease, and one of the major problems is for people in cold, damp homes where mould can grow."
So, what can you do to improve the air quality in your home?
1. Reduce the use of cleaning and decorating products
Some home cleaning and decorating products, including detergents, furniture polish, air fresheners, carpet and oven cleaners, paint, varnish and glue, can contain chemicals called volatile organic compounds (VOCs), like acetone, xylene and formaldehyde, which evaporate into the air when used or sometimes even stored, says the BLF. Products labelled allergy-friendly tend to have lower VOC levels, so try using those, or even just use a damp cloth if possible. Try to use solid or liquid cleaning products, rather than sprays, as when sprays get into the air, they can be breathed in more easily and can get further down your airways.
"Overuse of cleaning products should be avoided," advises Hopkinson, who says more rigorous research is needed before there's certainty about the effects of breathing in chemicals in homes, although about half of studies suggest being exposed to them increases the risk of developing allergies or asthma.
2. Ban tobacco smoke
If anyone smokes in your home, tiny particles from tobacco smoke can drift throughout the house and remain at harmful levels for up to five hours, says the BLF. If you smoke at home, smoke outside, close the door behind you and move away from the house. Or, even better, quit!
3. Ensure good ventilation
Always open a window when cleaning or decorating to ensure there's plenty of ventilation, so any pollution can escape outside. Allergy UK (allergyuk.org) points out that house dust mites need moisture, and ventilation will reduce humidity. Generally opening windows, particularly in the bedroom, will ensure good air flow throughout the house, and help expel pollution created in the home by heating and cooking. "Keeping homes as well ventilated as possible to reduce the build-up of moisture from bathing and drying laundry can help," says Hopkinson.
4. Purify your air
Allergy UK says running an air purifier continually, as per the manufacturer's instructions, can help to reduce/remove airborne allergens such as house dust mites, mould spores, dander, VOCs and smoke.
5. Keep floors and furniture clean
Pollutants like house dust mites and pet dander can settle on floors and furniture, so Allergy UK recommends carpets are kept clean using a vacuum with efficient pick up and filtration, hard floor surfaces are washed with hot, soapy water, and soft furnishings are washed regularly on a hot wash cycle.
6. Make your tile grouting water-resistant
In kitchens and bathrooms, Allergy UK recommends householders use water-resistant grouting for tiled areas, applied flush with the work surface to eliminate any chances of mould, which can cause respiratory problems.
7. Ventilate when cooking and heating
Cookers, heaters, stoves and open fires can release pollutants into your home, warns the BLF. They can release particulate matter (PM) - microscopic particles of dust and dirt in the air - and gases including carbon monoxide, nitrogen oxides and sulphur dioxide. Even when you cook with gas or electricity, tiny easily-inhaled particles are released, particularly when cooking with gas, which can release carbon monoxide, formaldehyde and oxides of nitrogen.
To keep such pollution to a minimum, make sure the house is well-ventilated and gas heaters and cookers have a flue, chimney, or other vent that releases the polluted air outside.
8. Sweep chimneys regularly
Burning wood and coal in a stove or on an open fire releases particulate matter. The BLF says this can irritate your nose and throat, giving you a cough or breathing problems. Studies show smoke from wood heating enters neighbouring homes, too. If you must burn coal or wood, says the BLF, make sure the chimneys are inspected and swept regularly by a HETAS-qualified sweep. Avoid buying a wood-burning stove or using an open fire if someone in your household has a lung condition. Install alarms for both smoke and carbon monoxide, and check the batteries regularly.
9. Service your tech
Dangerous, and potentially lethal, amounts of invisible and odourless carbon monoxide can be produced if cooking and heating appliances are faulty. The BLF advises householders to ensure such appliances are regularly maintained by a certified engineer. Install extractor fans over gas stoves and ranges, and always use them.
10. Use pea shingle for plants
Cover houseplant soil in plant pots with pea shingle, to stop mould settling and forming, suggests Allergy UK.
11. Be careful with candles and incense
Candles and incense sticks emit particles and other pollutants when they burn. According to the BLF, incense sticks emit more than 100 times the number of fine particles than a candle does. However, while one candle in a room can substantially increase the particle concentration in the air while it's burning, over a 24-hour period, the increase is minimal. Scented candles emit small amounts of formaldehyde and VOCs but if only used occasionally, they're unlikely to pose much of a health risk.
12. Watch your radon risk
Radon is a natural colourless and odourless radioactive gas that comes from rocks and soil. The radon level in air outside is very low, but it can be higher inside poorly-ventilated buildings, and high levels can cause lung cancer. The higher the level of radon, and the longer you're exposed, the greater the risk, warns the BLF. Indoor radon often varies from building to building. If your home is affected, UKradon has a tool to help you decide if you need to reduce the level and how - methods include creating a sump pit under the house, or introducing special types of ventilation.