Why indoor air is more polluted than outdoor air

Air pollution is often associated with big cities, traffic jams or industry. Today, however, a surprising and worrying reality is emerging: indoor air is frequently more polluted than outdoor air.

And yet, we spend almost 90% of our time in enclosed spaces: our homes, offices, schools and transport systems.

For people with allergies, asthma or sensitivities, this invisible pollution can have serious consequences for respiratory health.

Why is indoor air sometimes more harmful than outdoor air?

What pollutants are involved?

And above all, how can we improve indoor air quality in the long term?

Protech Allergies has put together a comprehensive guide to help you understand and take action.

A common misconception: indoor air is necessarily healthier

For a long time, the inside of the home was perceived as a refuge from outside pollution. However, numerous studies show that the concentration of pollutants can be 2 to 5 times higher indoors, and sometimes even higher.

This pollution is often :

invisible,

odorless,

continuous.

It therefore has a silent but lasting effect on the body.

The main sources of indoor air pollution

1. Fine particles (PM2.5 and PM10)

Fine particles come from :

outdoor pollution (road traffic, industry),

wood heating,

cooking,

candles, incense and fireplaces.

They enter the home through :

windows,

ventilation systems,

clothing and footwear.

Once inside, they accumulate and remain in suspension, especially in poorly ventilated spaces.

👉 PM2.5 is particularly dangerous, as it reaches the deep respiratory tract.

2. Biological allergens

Indoor air is a veritable reservoir of allergens :

dust mites (bedding, carpets, sofas),

pollens introduced from outside,

molds linked to humidity,

animal hair and dander.

Unlike outdoors, these allergens accumulate over time, especially if maintenance and ventilation are inadequate.

3. Volatile organic compounds (VOCs)

VOCs are chemical pollutants emitted by :

paints,

new furniture

glues and solvents,

household products,

home fragrances.

Among the best-known :

formaldehyde,

benzene,

toluene.

These substances can cause :

respiratory irritation,

headaches,

fatigue,

aggravation of allergies and asthma.

4. Everyday household activities

Certain everyday activities can have a serious impact on indoor air quality:

cooking without an efficient hood,

smoking indoors,

using sprays or air fresheners,

burning candles or incense,

cleaning with aggressive products.

Unlike outdoors, these pollutants do not disperse naturally.

Why does indoor air remain polluted longer?

Lack of air renewal

Modern homes are designed to be increasingly airtight to limit energy loss.

As a result, air circulation is reduced and pollutants accumulate.

Inadequate ventilation leads to :

increased concentration of pollutants,

stagnation of humidity,

proliferation of dust mites and mold.

Accumulation on surfaces and textiles

Unlike outdoors, indoor air interacts with :

carpets,

curtains

bedding,

sofas.

These elements act as reservoirs of pollutants, which are re-suspended with every movement.

The consequences for respiratory health:

Allergies and allergic rhinitis

Prolonged exposure to polluted indoor air promotes :

sneezing,

blocked or runny nose

irritated eyes,

chronic fatigue.

For allergy sufferers, symptoms often become persistent, even out of season.

Asthma and respiratory problems

Indoor pollution is a recognized factor :

triggering asthma attacks,

aggravation of respiratory symptoms,

reduced respiratory comfort at night.

Children and the elderly are particularly vulnerable.

Impact on sleep and well-being

Poor air quality can lead to :

waking up at night,

a feeling of "heavy" air,

morning headaches,

reduced concentration.

Why outdoor air can sometimes be less harmful

Outside, despite pollution :

the air is continually renewed,

pollutants are dispersed,

concentrations fluctuate more.

Indoors, on the other hand :

pollutants are confined,

sources are multiple,

exposure is prolonged.

👉 It's this continuous exposure that makes indoor air sometimes more dangerous.

How can we improve indoor air quality over the long term?

Ventilate intelligently

Ventilation remains essential:

open windows 10 to 15 minutes a day,

avoid peak pollution or pollen times,

ventilate after it rains.

Reduce sources of pollution

A few simple gestures:

limit the use of air fresheners and sprays,

choose mild household products,

avoid smoking indoors,

reduce the use of candles and incense.

Control humidity with a dehumidifier

The ideal humidity level is between 40% and 60%.

Above this level, the risk of mold and dust mites increases sharply.

The essential role of air purification

Despite all our best practices, it's difficult to completely eliminate pollutants without an air filtration solution.

The HEPA filter: an indispensable ally

A purifier equipped with a certified HEPA filter can capture :

fine particles (PM2.5),

pollens

dust mite allergens,

mold spores.

It's a key element for allergy sufferers and asthmatics.

Activated carbon against chemical pollutants

Combined with HEPA, activated carbon absorbs :

VOCs,

odors,

irritating gases.

It effectively complements mechanical filtration.

What's more, using a cordless vacuum with hepa filter will also help purify the air and ensure that dust doesn't spread.

A global approach to healthier air

At Protech Allergies, indoor air quality is part of a global strategy:

allergy prevention,

choosing the right equipment,

home maintenance,

raising awareness of best practices.

The aim is not just to purify the air, but to reduce exposure to pollutants over the long term.

Conclusion: regain control over the air we breathe

Although indoor air is sometimes more polluted than outdoor air, this doesn't have to be the case.
By understanding the sources of pollution, adopting the right gestures and using appropriate purification solutions, you can transform your home into a healthier environment.

Breathing better quality air means protecting your respiratory health today... and in the long term.