What's in my air
Mould spores — a moisture problem wearing an air quality costume
Mould spores are the airborne reproductive units of fungi, always present indoors at low levels, and multiplying wherever surfaces stay damp for more than a couple of days.
Limits and standards
India's NAAQS are ambient (outdoor) standards, and there is no statutory Indian indoor air quality standard for homes. WHO's guideline values are health-based targets rather than regulatory limits, and are consistently stricter.
| Standard | Limit | What it means |
|---|---|---|
| India | No regulatory standard | — |
| WHO Guidelines for Indoor Air Quality: Dampness and Mould | No numerical guideline; persistent dampness and microbial growth should be prevented | WHO explicitly declines to set a spore-count threshold, on the grounds that the evidence links health effects to dampness and microbial growth generally rather than to a measurable concentration of any species. |
Where it comes from
Monsoon humidity
Sustained high relative humidity allows growth on walls, wardrobes, leather and stored fabric without any liquid water present.
Condensation on cold surfaces
Air-conditioned rooms with humid outdoor air produce condensation on external walls and behind furniture — the classic hidden growth site.
Plumbing and seepage leaks
Bathroom seepage and leaks from the flat above are the commonest structural causes in Indian apartments.
Poor bathroom ventilation
A bathroom without an extractor fan holds moisture for hours after every shower.
Air conditioner drain pans and coils
A neglected split unit grows mould internally and distributes spores every time it runs.
Why it matters
- WHO associates indoor dampness and mould with respiratory symptoms, asthma exacerbation and respiratory infections, and its guidance is framed around preventing dampness rather than measuring spores.
- Mould allergy is a common perennial trigger, and unlike pollen it does not have a season in a damp home.
- The musty smell that people try to cover with air fresheners is microbial VOCs — an indicator that growth is active somewhere, often out of sight.
- Because the health basis is the dampness rather than a spore count, a purifier that reduces airborne spores has not addressed what WHO identifies as the problem.
Note
Can you detect it yourself?
Consumer air quality monitors are genuinely useful for tracking change and poor at absolute measurement. Knowing which of the two you are looking at prevents most of the disappointment in this category.
| Question | Answer |
|---|---|
| Can you sense it? | The musty, earthy smell is the reliable indicator, and it often precedes visible growth because the growth is behind or under something. Visible discoloration on walls, ceilings and grout confirms it. |
| What a consumer monitor shows | No consumer monitor detects mould. A hygrometer is the useful instrument: sustained relative humidity above 60% is your warning, and it costs a few hundred rupees. |
| Field test | Look behind wardrobes and beds against external walls, under sinks, and around window reveals. Most household mould is found by moving furniture rather than by testing air. |
| Laboratory test | Airborne fungal spore count and identification — Impaction sampling with culture or spore-trap microscopy (indicative ₹3,000–₹10,000) |
What removes it
Effectiveness ratings below describe the technology working correctly, within its service life, on water or air that suits it. “Depends” means there is a condition in the caveat that decides the outcome — read it before buying.
- Fixing the moisture sourceEffective
The only actual treatment. Leak repair, waterproofing, improved drainage, better ventilation. Everything else manages symptoms.
- Dehumidification below 60% RHEffective
Removes the condition mould requires. In coastal Indian cities during monsoon this is a dehumidifier's job, and it does more than any purifier will.
- Bathroom and kitchen extractionEffective
Removes moisture at the point of generation. An extractor run for twenty minutes after a shower prevents a great deal.
- Cleaning small growths with detergentPartial
For areas under about one square metre, wiping with detergent and drying thoroughly is appropriate, with gloves and a mask.
Caveat: Do not dry-brush. Wet the surface first, or you aerosolise spores from a contained surface problem into the whole room.
- HEPA filtrationPartial
Captures airborne spores effectively, which reduces allergen exposure while the source is being fixed.
Caveat: It is a support measure during remediation, not a solution. A purifier running against active growth is filtering a tap that is still on.
What does not work
Each of these is commonly assumed — or actively marketed — to help with mould spores. None of them do.
Air purifier as the fix
It removes spores from air while the colony continues producing them and while the dampness — which WHO identifies as the health issue — remains.
Ozone generators
Do not kill mould within materials at safe concentrations, and add a regulated pollutant. Widely marketed for mould and among the worst applications for it.
Bleaching visible growth on porous surfaces
Removes the colour and leaves the hyphae within the material. The growth returns, and the surface looks clean while the problem continues.
Air fresheners for the musty smell
The smell is microbial VOCs indicating active growth. Masking it removes the only warning signal you have.
Source control that beats filtration
For most indoor pollutants the highest-leverage intervention is not a device. These are the changes worth making before, or instead of, buying anything.
- Find and fix the water source. Check behind wardrobes on external walls, under sinks, around window reveals and on the ceiling below a bathroom.
- Keep relative humidity below 60%. Buy a ₹500 hygrometer before buying anything else.
- Run bathroom extraction during and for twenty minutes after every shower.
- Leave a gap between furniture and external walls so air can move behind it.
- Service split air conditioners annually — the drain pan and coil are common hidden growth sites that distribute spores through the room.
Frequently asked questions
Does an air purifier remove mould?
How do I stop mould in monsoon?
Is black mould dangerous?
Can I clean mould myself?
Sources
Every limit and standard quoted on this page comes from one of the documents below. Where a figure is not in one of these, we have not published it.
WHO Guidelines for Indoor Air Quality: Selected Pollutants
World Health Organization · published 2010-01-01 · checked 2026-08-01
Covers formaldehyde, benzene, carbon monoxide, naphthalene, nitrogen dioxide, PAHs, radon, trichloroethylene and tetrachloroethylene specifically as indoor pollutants.
WHO Guidelines for Indoor Air Quality: Dampness and Mould
World Health Organization · published 2009-01-01 · checked 2026-08-01
Concludes that persistent dampness and microbial growth should be prevented, and declines to set a numerical spore threshold.
This page states what published standards say and what the physics of each technology allows. It does not state what is in your supply — no page can. Where the two questions meet is a test result, and every entry in this library says which test to ask for.