Weird smell coming from insides

Has it ever been found why old MacBooks from 2010-2012, after some years, start emiting a smell commonly described as a combination of burning crayons/body odor?

It’s coming from my 13" mid 2010 MacBook Pro, and after cleaning several large internal components, mostly the main chassis and keyboard, it still smells.

After reading online, it might come from aging plastics or adhesives already going bad.

Just as long as they aren’t toxic fumes or harmful, I guess I’ll just bear it.

Can anything be done? Are these smells toxic or harmful?