What are the causes of mildew on walls?

Updated April 17, 2017

Mildew is a thin black or white-greenish growth produced by moulds. Mildew can be an ongoing problem in new houses, houses near coastal areas, houses in humid climates or houses with bad ventilation.


Mildew commonly appears in areas that are damp, warm, poorly lit and with little ventilation. Closet, cellar, crawl space and new house walls are all highly susceptible to mildew.


The moulds that cause mildew to form need moisture and certain temperatures to grow. Mildew will grow fastest at temperatures between 23.9 and 29.4 degrees Celsius.


Mildew is often spotty, causing discolouration and an unpleasant odour. It can cause mild to serious health problems if a person is continually exposed to it over a period of time.


Keep things clean and get rid of excess moisture in areas prone to mildew, by using air conditioning or a dehumidifier.


You may want to consider mildew-resistant paints or finishes that contain synthetic mildewcides on your walls to prevent mildew problems as well.

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About the Author

Lynn Holmgren is a freelance writer based in York, Penn. She has published articles about writing, international exchange, travel and outdoor recreation in ShowcasePA! magazine and Homgren also enjoys writing and reviewing short stories on her blog Long Story Short.