Someone thought this interesting enough to actually study it (Harvard and Stanford as a matter of fact — so this is where your research dollars go).
They took three groups of teens for two weeks: one group didn’t exercise, one group exercised then took a shower right away, and one group exercised then waited four hours before they showered (insert requisite sweaty teen joke here). They found that there was no difference in acne among the three groups.
Thanks to Harvard and Stanford, we now know the truth — body sweat does not make your acne worse.
Short, R. et al. Pediatric Dermatology, Volume 25, Number 1, January/February 2008 , pp. 126-128(3)