I think they can detect it in the pores, and avoid biting/stinging skin with those properties.
Long live garlic!
Yes, you don’t just metablize the stuff, it’s in the pores and everywhere else in the body after eating it. The active substance, allicin, is an organic sulfur compound so small that it penetrates cell walls. It also has antibacterial and anti-fungal properties, and possibly other ones we don’t know about yet.