What Could Spreading, Small, Inflammed, Red Bumps On Buttocks Suggest?

hello,

my husband had one small inflamed red bump on his buttocks the other day and now he has them all over his buttocks and spreading around his hips and going down his back legs...just under his bathing suit area for now. I counted about 25 so far. Looks like a small festered hair bump with a very small pin size blister in the middle. They do not itch. The only thing we can think of that is different...he has been drinking egg nog lately and has changed to new chemicals in our hot tub but I have been in there as well with no symptoms. It is Friday night and we are leaving to go on a week long cruise tomorrow. Please advise....Thanks so much!