I was preparing to paint the ceiling, when I found a lot of mould on top of the paint in the paint can. How?

How did this happen? what on earth made it possible? the lid was tightly on. Never knew paint would turn bad like that.


Matt Emulsion white ceiling paint, for those who wish to know. I was preparing to paint the ceiling, when I found a lot of mould on top of the paint in the paint can. How?
If it was black and swirly ..and not raised on it like a small mound..this will not be mold..it is simply the acrylics and polymers seperating from setting up...I was preparing to paint the ceiling, when I found a lot of mould on top of the paint in the paint can. How?
I haven't had paint that got mold on it but have had paint that turned very smelly, kind of a rotten egg/sulphur smell. It was paint I'd had around for a while, and usually paint keeps forever so I can't explain the ones that went off. I'm assuming this isn't paint you just bought. I wouldn't use it. Aside from anything else, it's likely to smell moldy even after it dries.
Weird. I wouldn't have guessed that could happen either. My suspicion is that the mold was growing on the natural latex in the paint, though it seems that the other chemicals in the paint would have killed the mold, but obviously not.