From an earlier post...
Garlic contains such high-sulfur compounds as alliin, allinase, and geranium. (Alliin and allinase combine in the body to form allicin.) European studies on garlic in treating various ailments typically administered about 600 mg garlic powder per day, about the same amount as in 1.5-2.5 cloves of raw garlic. "Odorless" garlic supplements are enteric-coated to survive stomach acid, in which they dissolve in the gut instead of the stomach. This helps relieve "garlic breath."
But once you dump all these sulfur compounds into the gut, it's probably inevitable they'll wind up in the bloodstream (which is the purpose of digestion, of course), and subsequently, the pores and skin. From Prevention magazine, "But if you eliminate the smell, will you also eliminate garlic's therapeutic powers? The answer seems to be yes, says Barbara Klein PhD, professor of food and nutrition at the University of Illinois in Urbana. Although many companies are trying to grow odorless garlic, no one has yet proved that it's possible to have the health benefits without the aroma (and therefore the sulfur compounds).