I thought this would be a pretty easy question to answer. The kind of thing where all I'd have to do would be to check the dictionary and bang, there's the answer. No such luck. Not even close. Apparently, the difference between mold and mildew has become something of a hot-button issue, especially for mycologists.
Many mold remediators -- the people you have to call if your house or your industrial building is infested with nasty mold -- will tell you there's no difference between mold and mildew. They write this on their websites and in their FAQs as if to tell the dumb public to quit asking questions and just let the professionals get to work. So I suspected that there really is a difference between the two, and I kept searching.
Here's what I understand so far:
- Both mold and mildew are types of fungus.
- Mainly, molds grow on decaying organic material, including carpets, ceiling tile, drywall, paper, wood, old bread, etc. There are over 150 species of molds.
- Mildew, on the other hand, grows specifically and exclusively on plants. From what I've gathered, there are three types of mildew, though most often they are either the downy or powdery varieties. Mildew generally produces a whitish, fuzzy coating over the top.
Mildew on a honeysuckle leaf
photo from Purdue Plant & Pest Diagnostic Laboratory
You don't even want to see pictures of mold, not even for comparison's sake.
Or anyway, when I looked at some, they made me feel all creepy-crawly.
- Some molds can grow on plants, but mildew only grows on plants.
- Because mildew only grows on plants, that stuff in your shower and bathtub is not mildew. The cleaning products industry wants you to think it's mildew, but it's actually mold.
- If you call up a mold remediation person and say, "I've got mildew all over the inside of my shower," the mold remediation person will understand that what you mean is you have a certain type of mold that you've been trained to call mildew in your shower. It's probably not the same kind of mold that might be growing on the backing of your carpets or in the walls in your attic, but it's another kind of mold that likes to grow in showers.
- I'm not sure why the cleaning industry salespeople want you to think it's mildew. Perhaps they discovered that consumers like the word "mildew" better, or that people think it would be easier to clean than mold, or something like that. Perhaps the companies want you to think you need one product to take care of mildew and another product to clean up mold. Or perhaps people may suspect that a bleach-based cleaner in a fancy bottle with a trigger won't really do anything about mold, but those same people might believe that that same fancy bottle with the trigger might be able to do something about mildew.
- Both molds and mildew love moisture. The only way to get rid of mold for real is to get rid of the moisture that it needs to survive. That means fixing the leak or stopping the drip or otherwise reducing the relative humidity of the area to below 50%. You can spray stuff on the mold in your shower, and it will look like it's gone, but unless you get rid of the source of the moisture, the mold will keep coming back.
- Professionals who know about cleaning up & killing mold say that bleach is actually a bad thing to use on mold. The same way that antibiotics and antibacterial soaps can create more problems, bleach can create "zones of inhibition." Essentially this means that bleach can kill off the good stuff but it doesn't entirely kill off what you don't want, so then the bad stuff (mold) comes back with an even greater vengeance.
- Even though I've been a strong believer in the powers of bleach for years, I think I might make the switch to borate-based stuff for cleaning my bathroom. I don't know if there's anything like that available in yon grocery store or not, but I'm going to look.
NACHI, National Association of Certified Home Inspectors, Mold/Fungus in attic space discussion, pages one and two
FYI - Mold & Mildew, Home & Business Inspection Services LLC
Toxic Mold Help, mold vs. mildew discussion topic
Health & Energy, Mold Prevention
Black-Mold.com, Mold Definitions