I have been using borosil lunch box from few months, Borosil lunch box

After few days of using it there are few black spots started generating at the plastic lid, I tried removing them using dishwashing soap and even trying to remove it by rubbing hard but nothing happened.
Could anybody tell me what is this deposit and how could I get rid of this. Black spots in rubber rim

  • Did you microwave that? It might be a fungus as the current answer suggests, but I wonder if it is imperfections/contamination in the plastic that reacted badly to being microwaved. Also, have you tried a diluted bleach cleaning? Commented Oct 11, 2018 at 14:11

3 Answers 3


It may be fungus. If so, soaking it in vinegar for about 15 minutes and then washing it as regular should do. The discoloration may not disappear completely, though.

  • unfortunately it didn't worked
    – Amit Bisht
    Commented Oct 7, 2018 at 11:32

This is mildew, a form of mold. The black stains it produces are practically impossible to remove from plastic objects.


Use ammonia first then scrub with a brush.
Then try baking soda, scrub with a brush.
Lastly soak in bleach rinse with water while scrubbing with a brush.

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