FTA:

Freshly secreted sweat has little odor, because the long-chain fatty acids the axillaries secrete are too big to be volatile, says first author, Chris Callewaert of Ghent University, Belgium. Bacteria break these, as well as hormones and sulfur compounds, down to waftable sized, odoriferous molecules.

On the clothes, the main culprit bacteria are micrococci, says Callewaert. “They are known for their enzymatic potential to transform long-chain fatty acids, hormones, and amino acids into smaller—volatile—compounds, which have a typical malodor.”

Staphylococci, however, do not create the same odor (but do not grow on polyester as well):

Staphylococci, which inhabit both axillary skin and adjacent textiles (the latter with much less diversity), create a normal, non-malodorous body odor, he says.