Small patches of mould caused by condensation can usually be cleaned safely yourself. The government's guidance says that while "smaller instances of damp and mould may be removed by a tenant or landlord", larger areas "will require professional removal". Here are the signs you are past the DIY stage.
1. It covers more than a small patch
If mould has spread across a large part of a wall or ceiling, or into several rooms, cleaning it yourself means disturbing a lot of spores and is unlikely to deal with the cause. Get it looked at.
2. It keeps coming back
Mould that returns within weeks of cleaning is a symptom. The cause might be an extractor fan that doesn't work, a cold spot where insulation is missing, a slow leak, or water getting in from outside. Cleaning alone won't fix any of those.
3. There's water getting in or leaking
Tide marks, bubbling plaster, a patch that gets worse after rain, or damp near pipes, radiators or a bath all suggest penetrating damp or a leak rather than condensation. The repair may need a roofer, builder or plumber as well as a mould specialist.
4. Someone in the home is at higher risk
The government's health guidance lists the people most likely to be badly affected by damp and mould: people with asthma, COPD, cystic fibrosis or other health conditions, people with weakened immune systems, pregnant women and new mothers, children, older people, and people who are housebound or have mobility problems. If that includes anyone who would be doing the cleaning, or who lives in the home, don't take chances. If someone is unwell, speak to a GP or call NHS 111.
5. It's in materials you can't clean
Mould that has got into plaster, wallpaper, carpet, soft furnishings or wood often means the material needs removing, not wiping. The same goes for anything damaged by a flood or by dirty water, such as a sewage leak.
What a professional will do
A good specialist starts by finding the cause, then removes the mould and damaged materials safely, and explains what needs to change to stop it coming back. See professional mould and damp treatment for typical steps and costs, and choosing a specialist for the questions to ask.
If you rent
Damp and mould caused by the building is normally your landlord's responsibility. Report it in writing before paying for any work. See who has to fix damp and mould in a rented home.
Sources
- Understanding and addressing the health risks of damp and mould in the home, GOV.UK, updated 1 April 2026