Have you ever been in a damp and humid bathroom that had thin layers of black film in cracks and crevices? You may have even smelled an unpleasant odor. If so, then you’ve met mildew.

Mildew is not quite as straightforward as some people think, though. The word “mildew” is used to refer to different types of molds and fungi. Some of these can be very different than what most people think of as mildew.

For example, gardeners and scientists use mildew to refer to powdery or downy mildew, which is made up of various species of fungi that grow on plants. These types of mildew grow on plants as parasites and can be very harmful to crops. They look like white or gray dots on plants.

More commonly, though, most people say mildew when referring to mold growth. Sometimes you even hear the two words used together: mold and mildew. Although both are forms of mold, we usually use mold to describe mold that grows on food. Mildew is usually used to describe mold that grows on objects, such as shower walls, paper and clothing.

Mildew likes to grow in hot and humid (moist) conditions. A damp shower in a house heated up by the summer sun is the perfect spot for mildew to grow and multiply quickly.

The particular black mildew that likes to grow in showers is usually Stachybotrys chartarum, which is a specific type of mold. In addition to being ugly to look at, it also produces a strong musty odor that often tips off people to the presence of mildew.

Mildew is not something you want to treat lightly, as it can be harmful to your health. Some mildew contains toxins — called mycotoxins — that can cause allergic reactions or illnesses in certain people. Mildew can cause a wide variety of problems, including headaches, coughing and irritation in the eyes and throat.

So how do you get rid of mildew? Once you see it, you need to remove it. Bleach is one of the most popular cleaners used to kill mildew. You can also use vinegar or a wide variety of mildew cleaning supplies sold at the store.

After you get rid of mildew, you’ll want to keep it from returning. In a hot and humid area, you may want to consider removing as much moisture as possible. Using an exhaust fan in the bathroom and wiping down shower walls after a shower help a lot. Some people also use machines called dehumidifiers to help dry the air.


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  1. Dear Wonderopolis,

    I loved today’s wonder! I think tomorrow’s wonder of the day is about weather changing.

    Remember back on wonder of the day #567 – What’s so great about going green? I thought wonder of the day #568 was about libraries and I was right. Wonder of the day #568 was about libraries. Wonder of the day #568 was Where is the largest library in the world?


    • Happy Saturday, TJ! We’re happy to hear from you today!

      SUPER JOB on guessing about Wonder #568! It was SO AWESOME to learn about the Library of Congress! We hope you have a GREAT weekend full of WONDER! :-)

    • We think you’re an AMAZING Wonder Friend for guessing, Annie! Thanks for visiting today’s Wonder and letting us know what you think tomorrow’s Wonder will be about, too! :-)

    • We’re super glad you liked the video for this Wonder of the Day® about mildew, Shayla! Thank you for sharing that with us today, and THANK YOU for being an AWESOME Wonder Friend! :-)

    • We’re glad you learned something new in Wonderopolis today, Caelah! Thanks for letting us know you visited this Wonder of the Day®! :-)

  2. We once had to sleep in a hotel on a vacation. The room felt a tad bit humid, which I thought was odd. When I woke up the next morning my eyes we’re blood shot and my throat was burning.

    • Thank you for sharing your personal connection to this Wonder, Clayton! We’re super sorry you had to go through that, and we hope you felt better quickly! We appreciate that you stopped by this Wonder of the Day® today! :-)

    • Hi, Jaquaisa! Thank you for stopping by this Wonder of the Day® and sharing what you think about it! We hope you have a WONDERful day! :-)

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Have you ever wondered…

  • What is mildew?
  • Where does mildew like to grow?
  • Can mildew be unhealthy?

Wonder Gallery

Try It Out

Ready to clean? Your parents can always use a little extra help around the house. We think the best way to learn more about mold and mildew is to go on a mold and mildew safari around your own house.

Mold and mildew likes to collect in places that get a lot of moisture. Do you have a basement? If so, check down there!

You’ll also want to check in bathrooms, particularly around showers and bathtubs. You may also find mold and mildew around windows or doors.

Search high and low to find any mold or mildew that may exist in your house. When you’ve found some, do something about it!

Make your own homemade mold and mildew remover (get a parent’s help with this part!) and then get to work! You’ll want to have some rubber gloves, a brush and a dry towel, too.

Spray your homemade mold and mildew remover on areas where you can see mold or mildew. Let it sit for about five minutes or so. Then start scrubbing! When you’ve scrubbed away the mold or mildew, rinse the area with water and dry it thoroughly. To keep mold and mildew from returning, try to keep that area dry in the future.


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Explore Science NetLinks’ Germs and the Body lesson to learn about where germs exist, how they can get into and affect the body and how the body defends itself against them.


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