I've went as long as seven days without a shower. As Gandar says, in those cases, I've washed those areas that have folds or creases (and it helps to use an antibacterial soap). I have gone three days not even doing that. Washing is overrated in a survival situation, unless it's going to be long-term. The ladies probably can't get the same mileage, as Tess washes up every day no matter what. I also wouldn't waste water washing hair, even though I have shoulder-length hair, the dirtier and greasier it gets, the easier it is to comb it and get it to stay put out of your face.
I will admit that once you have a chance to get clean again...it does feel good.