Fun fact: The alkali dust that makes up the playa surface is extremely basic (as opposed to acidic) and has many properties of soap, so in essence it keeps you clean and germ free. I usually take 2 showers over the course of the week, and it's not because I feel a need to clean myself, more like it just feels refreshing as fuck to dump water all over yourself in the middle of a hot day.
Second, it's so goddamn dry out there that sweat evaporates before you even feel it, so bacteria never grow under your armpit and keeps the smell low. That's not to say people don't smell at all there, but the average construction site downtown has worse BO overall than Burning Man.