Eli5: Why do some smells like fuel oil or garlic stay on hands for hours even after extensive scrubbing and washing?
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Some chemicals are “hydrophobic”, meaning they’re either less likely to be miscible (able to mix with) water, or are outright repelled by water, refusing to interact with it at all.
Oil is an example of this. Oil doesn’t mix with water well, and fuel oil is just a kind of oil. Garlic has oils in it and those are also hydrophobic.
Washing may help, but it may not be 100% effective unless you use hot water and lots of a good soap. Soap interacts with oils and grease to “capture” particles of it and keep them from re-adhering to a surface, and is why soap is so effective at cleaning. Using the hottest water you can stand will also help by making the oil thinner and more soluble (able to mix with other liquids).
But in the end there’s lots of areas for small amounts of very actively odorous compounds to stick on your hands, and even within the first few layers of your skin or around hair follicles, etc. So you may detect traces of an odor even after washing.
Another good reason to wash your hands often with hot water!
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