Dust, allergens and indoor air

People in most countries spend the overwhelming majority of their time indoors, which makes indoor air quality a larger determinant of exposure than outdoor air for most of the population.

What household dust is

Studies of domestic dust find a consistent mixture: fibres from textiles, skin cells, soil tracked in on shoes, food particles, pet dander, dust mite matter, and chemical residues that adsorb onto particles.

The soil component is substantial, which is the argument for removing shoes at the door — a practice that reduces both dust and the contaminants it carries.

Reducing dust

The measures that work, roughly in order.

Shoes off at the door, with a good doormat inside and out.

Vacuuming with a sealed machine and a fine filter, since a poorly sealed vacuum redistributes fine particles rather than capturing them.

Slow passes are more effective than fast ones.

Damp dusting rather than dry, which captures particles instead of launching them.

A microfibre cloth used dry works similarly by holding particles electrostatically; a feather duster does the opposite.

Cleaning high to low, so that disturbed dust is caught rather than resettling on cleaned surfaces.

Reducing the surfaces that hold dust — open shelving full of objects, heavy drapery, deep pile carpet — which is a legitimate argument for a simpler arrangement in an allergic household.

Washing textiles — bedding, cushion covers, curtains, soft toys — since these hold a great deal.

Filtering the heating and ventilation system, where one exists, and changing the filters at the stated interval.

Dust mites

Which are a genuine allergen for a substantial minority.

They feed on skin cells and require humidity above roughly half to thrive.

Which means the effective measures are reducing indoor humidity through ventilation, washing bedding at high temperature weekly, using barrier covers on mattresses and pillows, and reducing soft furnishings in bedrooms.

Freezing soft toys that cannot be hot washed kills mites.

Evidence for individual measures in isolation is mixed; combined approaches perform better.

Ventilation

The single most effective intervention for indoor air generally.

Modern buildings are sealed for energy efficiency, which without adequate ventilation concentrates moisture, carbon dioxide, cooking emissions and volatile compounds.

The measures: use extract fans during cooking and bathing and for a period afterwards; open windows briefly and widely rather than continuously and narrowly, which exchanges air with less heat loss; do not block trickle vents, which are there deliberately; and consider mechanical ventilation with heat recovery in very airtight properties.

Sources worth reducing

Where the emissions come from.

Cooking, particularly frying and gas cooking, which produces fine particles and nitrogen dioxide.

Extraction that vents outside rather than recirculating is substantially better.

Candles, incense and open fires, which produce fine particulate matter in quantity.

Cleaning products and air fresheners, which emit volatile organic compounds; some react with indoor ozone to form secondary pollutants.

Fragrance-free products and ventilation while cleaning reduce exposure.

New furnishings, paints and flooring, which off-gas for a period, and where low-emission products and ventilation during and after installation help.

Damp and mould, which is discussed at length elsewhere on this site and which is a significant respiratory exposure.

Air purifiers

Where the evidence sits.

Filtration units with genuine high-efficiency filters do reduce airborne particulate matter measurably, and trials in allergic and asthmatic populations have found symptom benefits in some studies.

The unit must be sized for the room and run continuously to be useful, and filters must be replaced.

Devices generating ozone or ions are a different category, and ozone generation in occupied spaces is advised against by health authorities.

A purifier does not substitute for ventilation, since it does not address carbon dioxide or gases.

Plants

Worth addressing since the claim is persistent.

The frequently cited research was conducted in sealed chambers, and subsequent analysis has found that the air exchange in a real room dwarfs the effect, requiring implausible numbers of plants to matter.

Plants are worth having for other reasons, and are not an air quality measure.

General information only, not medical advice. Consult a qualified professional about allergies, asthma or respiratory symptoms.