Its more like social stigma for me. I'll not shower if no one was going to get close enough to me to smell me.
I have driven across the country and the westward run I made the whole 4 day run without a shower. Coming back was 6 days and again I did it without I think. I think I used a few wet wipes and dry showered on day 3 only to find that it made my underarm smell worse.
Its doable just from my perspective, just that other people getting near me would be what makes me shower.