How to Get Rid of Mould Smell
Published 5 December 2025 by AirFresh Mould Removal London.
How to Get Rid of Mould Smell
That persistent musty smell in your home is not just unpleasant—it is a warning sign. The distinctive dank, earthy odor commonly described as "mouldy" or "musty" indicates active mould growth producing microbial volatile organic compounds (MVOCs) that affect both property and health.
This guide provides IICRC S520-compliant information on mould odors: what causes them, why masking strategies fail, and why professional source removal following the ANSI/IICRC S520-2024 Standard for Professional Mold Remediation is the only permanent solution.
Critical principle: You cannot eliminate mould smell without eliminating mould growth. Air fresheners, odor absorbers, and cleaning products mask the problem temporarily—they do not address the source.
What Causes Mould Smell: Understanding MVOCs
The musty odor associated with mould is caused by microbial volatile organic compounds (MVOCs)—gaseous byproducts produced during mould metabolism and growth.
The Science of Mould Odor
As mould forms, grows, and spreads, it metabolizes organic materials (wood, paper, cellulose, dust, fabric) and releases chemical compounds into the air. These MVOCs are responsible for the characteristic "mouldy" smell.
MVOC composition includes:
- Alcohols (including ethanol, 1-octen-3-ol, 2-octen-1-ol)
- Ketones, aldehydes, and esters
- Carboxylic acids and lactones
- Aromatic hydrocarbons and terpenes
- Sulfur and nitrogen-containing compounds
Why MVOCs are so detectable: MVOCs have extremely low odor thresholds, meaning humans can smell them at very low concentrations. This is why even hidden mould can produce strong odors—the gaseous compounds diffuse through walls, floors, and ceilings.
Mould Smell Descriptions
People describe mould odor differently, but common descriptions include:
- Musty: Like old books, damp basements, or closed attics
- Earthy: Soil-like, organic decomposition smell
- Dank: Wet, stale, unpleasant dampness
- Sour: Fermented, acidic quality
- Mildew-like: Similar to wet towels left in washing machine
If you smell any of these odors persistently in your home, mould is almost certainly present—even if not visibly obvious.
MVOC Health Effects
Beyond being unpleasant, MVOC exposure can cause health symptoms:
- Headaches and dizziness
- Nasal irritation and congestion
- Sore throat and fatigue
- Nausea and eye irritation
- Exacerbation of asthma and allergies
IICRC S520 and Condition 2: When Odor Indicates Hidden Contamination
Under the ANSI/IICRC S520-2024 Standard, persistent mould odor without visible growth may indicate Condition 2—an indoor environment contaminated with settled spores from hidden mould source.
This means: Strong mould odor without visible mould does NOT mean "no problem"—it means professional investigation is required to locate hidden source.
The mould producing the odor may be behind walls, under flooring, in HVAC systems, in wall cavities, above ceilings, or in crawl spaces—completely hidden but actively growing and releasing MVOCs.
Common Sources of Mould Smell in UK Homes
Bathrooms
Common locations:
- Beneath/behind bathtubs (hidden leaks)
- Shower enclosures and tile grout
- Bathroom ceilings (condensation damage)
- Under bathroom flooring (slow leaks)
- Behind wall tiles (moisture penetration)
Basements and Cellars
Common locations:
- Concrete walls with rising damp or penetrating damp
- Under stairs and in corners (poor air circulation)
- Stored items (cardboard boxes, old furniture)
- Behind stored items against walls
Walls and Ceilings
Common locations:
- External walls with poor insulation (cold spots, condensation)
- Behind wallpaper (moisture trapped, hidden growth)
- Around windows (condensation, failed seals)
- Ceiling corners (temperature differences)
HVAC Systems and Ductwork
Problem: HVAC contamination distributes mould spores and MVOCs throughout entire property. Under IICRC S520, HVAC contamination requires specialized remediation.
Why Odor Masking Fails: The IICRC S520 Source Removal Principle
The ANSI/IICRC S520-2024 Standard is unequivocal: source removal is the fundamental principle of mould remediation.
Common Odor Masking Strategies That Fail
❌ Air Fresheners, Scented Candles, Essential Oils
These products mask odor temporarily by introducing stronger scents. They do NOT eliminate MVOCs or address mould growth. Once the masking scent dissipates, mould odor returns.
❌ Odor Absorbers (Baking Soda, Activated Charcoal)
While these substances can absorb some odor molecules, they cannot keep pace with continuous MVOC production from active mould growth.
❌ Spraying Biocides or "Mould Killer" Products
IICRC S520-2024 Section 2 explicitly advises against "simply spraying mold-contaminated areas with chemicals without first physically and completely removing the mold."
❌ Fogging or Misting Antimicrobials
S520-2024 explicitly states "remediators should not mist or fog disinfectants in lieu of source removal."
❌ Ozone Generators
IICRC S520 Section 9.1.7 states ozone should not be relied upon as primary remediation tool. Ozone is also hazardous to humans, pets, and materials.
The Only Permanent Solution: Source Removal
According to IICRC S520 principles:
- Locate the mould source (may require professional investigation)
- Correct the moisture source (leaks, condensation, humidity)
- Physically remove the mould through cleaning or material disposal
- Clean and HEPA vacuum all affected areas
- Verify successful remediation
When Professional Remediation Is Required
The NHS and IICRC S520 recommend professional intervention when:
- Mould odor persists despite cleaning visible growth: Indicates hidden contamination
- Strong musty smell but no visible mould: Requires professional investigation
- Musty odor in multiple rooms: Indicates extensive contamination
- Visible mould exceeds 1 square metre
- Health symptoms correlate with odor: Headaches, respiratory symptoms
- HVAC system suspected: Musty air from vents
Temporary Odor Management While Awaiting Professional Help
1. Ventilation (Most Important)
- Open windows and doors to dilute MVOC concentration
- Use fans to increase air movement
- Run extractor fans continuously in affected rooms
2. HEPA Air Purifiers
- HEPA filtration captures airborne mould spores
- Activated carbon filters can adsorb some MVOCs
3. Dehumidifiers
- Reduce indoor humidity below 60% RH
- Target 30-50% RH
Preventing Mould Odor: Long-Term Moisture Control
IICRC S520 Section 3: "If the source of moisture is not identified and corrected, mold growth will likely recur."
UK-Specific Moisture Control Strategies
- Keep trickle vents open 24/7
- Use extractor fans during and 15-20 minutes after bathing/cooking
- Open windows daily for 10-15 minutes minimum
- Target 30-50% RH indoors with dehumidifiers
- Maintain consistent heating 18-21°C
- Fix plumbing leaks immediately
Frequently Asked Questions
Can I get rid of mould smell without removing mould?
No. Under IICRC S520 principles, mould odor (MVOCs) is produced by active mould growth. The only way to permanently eliminate odor is physical source removal. Air fresheners and odor absorbers may temporarily reduce smell, but MVOCs continue production until mould is removed.
Why does my house smell musty but I cannot see mould?
This indicates Condition 2 under IICRC S520—hidden mould contamination. MVOCs are gaseous and permeate through building materials. Mould may be behind walls, under flooring, in HVAC systems, or in crawl spaces. Professional investigation with moisture meters and thermal imaging is required.
How long does mould smell last after removing mould?
After proper S520-compliant remediation (physical source removal + moisture correction), residual odor typically dissipates within days to 2 weeks. If strong odor persists beyond 2 weeks, remediation was incomplete or hidden sources remain.
Can mould smell make you sick?
Yes. MVOCs themselves cause health symptoms: headaches, nausea, dizziness, nasal irritation, fatigue, eye irritation. These effects occur even without direct mould spore exposure.
Will bleach remove mould smell?
Bleach kills surface mould but violates S520 source removal principles because it does not physically remove contamination. Dead mould, spores, and mycotoxins remain. Bleach cannot penetrate porous materials where mould roots persist.
Professional IICRC S520-Compliant Mould Odor Remediation
We understand that persistent mould odor indicates a problem requiring professional source removal. As IICRC-certified specialists following ANSI/IICRC S520-2024 standards, we provide comprehensive assessment and remediation that permanently eliminates mould and odor.
Call us to discuss whether odor indicates simple moisture management needs or hidden contamination requiring remediation. You can also send photos for a quick assessment.
Book your professional mould assessment →
Disclaimer: This article provides educational information about mould odors and IICRC S520 remediation standards. It is not a substitute for professional mould assessment. Property owners with persistent musty odors should consult IICRC-certified mould remediation professionals.
Last Updated: December 2025