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Mold on Cups

by Joslyn

Question :

A reader asked the following question through our “Ask a Mold Question” section of our site :


Can mold grow on plastic cups that have been washed and stacked together but not dried completely?

As long as either food or juice particles are not left in the cups, mold should not grow in the stacked cups.

However, it does start to smell if left stuck together like that for a while – mostly because the water gets stagnant, heats, and grows bacteria.

So even though it is not probable that mold will grow, stacking wet cups together creates the perfect habitat for bad bacterias.

And it warps plastic cups!

So overall, its best to stay away from stacking wet cups =]!

Answer :

How about mold growth when putting the flow control of a childrens sippy cup together when it comes out of the dish washer and it’s not completely dry? Would the same concerns follow it as well as the cups? I just wonder that since it makes a tighter seal if there is more concern of mold growth. I like to put them together when they come out of the dish washer so I don’t lose them. Thanks for your help!

Sippy cup pieces, you have to be really careful with.

The same thing applies as far as mold growth goes, though the chances that the inside of the piece will grow mold is much higher only because its a smaller area and juices etc go through the holes.


Watch for “souring” of the pieces, and make sure that all particles of juice or anything else are thoroughly cleansed.

A good idea would be to run one of those wirebrushes through each hole if its possible.

As far as drying it – as long as the pieces are not smelling “sour” or changing colors – they’re probably just fine. Just use your best judgement! =]

Further Recommended Reading :

Joslyn from the MoldBlogger team

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