system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does garlic smell good in food but bad in breath?
gpt
As you are eating it, your body begins breaking down garlic immediately into sulfuric compounds.  These sulfuric compounds remain in the mouth and smell very similar to the compounds that the bad breath causing bacteria in your mouth also create. 

Secondary to that, as the garlic passes into your digestive tract, your body decomposes garlic into allyl methyl sulfide.  This is distributed through the bloodstream to the lungs, then exhaled through your mouth or you just burp it up.  This is what causes garlic breath to linger even after brushing your teeth, mouthwash, etc. 

It smells pungent and aromatic as a food while also being slightly sweet if cooked.  The chemical reaction that occurs  during digestion is what makes it no longer appealing after we eat it.