It is stressful and strips the natural oils off their feathers, but with battery hens little space given for each hen, It wont hurt initially.
I found a pullet my neighbor let go who was full of mites, dirty and i think the fleas were bothering her, and I covered her face and sprinkled dome diatomaceous earth on her, and seemed to help her, but never had to bathe her, Chickens with ample space tend to keep themselves clean.
The poorly kept chickens i spoke about in my last post thrived once they got to free-range a little, and lived a long healthy life on my neighbors farm once we moved back to a house where we couldn't have them.