Mold at Home: Just the Figures
Mold at Home: the whole thing in five minutes, for when you want the numbers and nothing else.
Fungi that grow on damp surfaces indoors, often after leaks, flooding or high humidity.
Key takeaways
- Indoor humidity target: below 60%, ideally between 30% and 50%
- Dry wet materials within: 24 to 48 hours to prevent mold growth
- Most useful single change: Fix leaks in roofs, pipes and windows as soon as possible.
- Commonest mistake: Painting or caulking over mold.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
The numbers, in one place
| Measure | Figure |
|---|---|
| Indoor humidity target | below 60%, ideally between 30% and 50% |
| Dry wet materials within | 24 to 48 hours to prevent mold growth |
| Small areas you can clean yourself | up to about 10 square feet |
| Testing to identify the type of mold | usually not needed; remove it whatever the type |
In one paragraph
Damp and moldy homes are linked to stuffy nose, wheezing, coughing and worse asthma, and the key to control is controlling moisture.
Worth doing
- Fix leaks in roofs, pipes and windows as soon as possible
- Use exhaust fans in bathrooms and kitchens and a dehumidifier in damp areas
- Scrub mold off hard surfaces with detergent and water, and dry completely
- Wear an N95 respirator, gloves and goggles when cleaning moldy areas
- Throw out porous items such as carpet padding or ceiling tiles that stay moldy
Worth avoiding
- Painting or caulking over mold
- Mixing bleach with ammonia or other cleaners
- Cleaning large or flood-damaged areas yourself if you have asthma or a weakened immune system
Related topics
- What the Guidance Really Says About Asthma and Allergy (Allergies)
- Air Quality: What the Evidence Actually Says (Respiratory Health)
- What the Guidance Really Says About Flood Water Safety (Heat, Cold and Weather Safety)
- The Evidence on Occupational Asthma, Without the Hype (Workplace Health)
Where to go next
- What People Get Wrong About Mold at Home
- Starting Out With Mold at Home
- Mold at Home — the reference entry
- Environmental Health: The Complete Guide
- What the Guidance Really Says About Drinking Water and Private Wells
- What the Guidance Really Says About Air Pollution and the AQI
When to speak to a doctor
See your doctor if you have wheezing, worsening asthma, a lasting cough or nasal symptoms that improve when you are away from home, or if you have a weakened immune system and live with mold. Call 911 for severe trouble breathing or an asthma attack that does not respond to your rescue inhaler.
Where this comes from
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.
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