I have two rules about baths - first they should be deep and second they should be hot. As hot as you can manage - hot enough to turn your skin scarlet.
This also is an invaluable relapse indicator, as I am one of those people whose symptoms are exacerbated by the heat. The stressful time before Christmas when my Dad died coupled with the dreadful cold I had over Christmas were prime relapse triggers. I have been suspecting for some time as my feet and hands have got more numb (they were almost better too). Unfortunate by product of numb feet more falling over and more bruises... hence desire for long hot arnica filled bath. Sadly after five minutes it became apparent I also have a dose of ON in my left eye as the vision had dulled to the extent that I could hardly see out of it. Ten minutes in the cold of the pink room and the landing everything has calmed a little. The itching on hands and feet has stopped (how can they itch when they are numb?) and the eye is back to only dimming the colour red. Happily I am seeing my Nurse a week Monday so we can discuss it all then.
Talking of baths, I also have two preferences (they cannot be classed as rules) in respect of bathing - first baths should be lengthy (my preference is for wrinkly skin and the water turning cold) and second they should be cat free. Tinker's fascination with water makes this hard, if he's locked out he'll scratch at the door and pull up the carpet and if he isn't locked out he'll let himself in and try to join you in the bath. Length is curtailed by the unpleasant relapsing effect on my symptoms.