Probably not an answer to your question, but it needs to be said. For males, fertility might be a concern in hot baths:

http://www.medicalnewstoday.com/articles/64481.php

I can't imagine any other issues. Hot tubs are pretty damn effective damn at stress relief.

I'm sure some paleo recreationists might argue that the majority of our paleo ancestors didn't have access to hot or even warm water but I don't think that argument really flies any more.

Personally, I'd say no. All those positive benefits of cold water don't say anything about hot water being bad. I used to be a cool shower person but when I lost 100 lbs last year (on a decidedly non-paleo diet plan - I'm better now!) I felt pretty cold all the time and upped the temp on my showers.

I know during my marathon training we were told to take a cold shower or bath immediately after, even if we REALLY, REALLY wanted a hot one because it would help with our muscle soreness. I'm not sure of the reasons why. I know when I did listen to them I could tell the difference. There was definitely less muscle soreness with a cold shower/bath following a long run. I hated it though.

Someone was telling me recently that native Siberians and Finnish people (and maybe others in the north) would bathe in hot water or use a sauna/sweat type thing pretty frequently, to keep their core body temperatures up. I guess that doesn't really apply to us these days, but it's a thought. Hot steamy showers are really wonderful to stay invigorated during cold winters (especially when you keep the heat down in the house to conserve energy)!

I bathe every day in as hot water as I can take. No idea why, just like to do it.

(Probably not a helpful answer, but wanted to advance the discussion with my personal experience.)

If it's supposed to be bad, then why does it feel so damned good!?!

(same line as for sex..)

Well, toxins more readily dissolve in hot water, so I suppose you'd have slightly more toxic water if it were hotter. I'd say it's more important to have shorter/less frequent showers instead of colder ones, since you're exposed to far less in the way of chlorine etc.

My thinking is to not worry about what books or doctors or what anyone else says, and just do whatever feels good. I've had a bad head cold for the last few weeks, and the hot shower with all of the steam it's been the best feeling, and it helps relax my muscles. It can definitely affect my body temp and it can take a while to adjust, but the change seems more positive than negative.

I have strong feelings about not one single diet being right for all people or at all times in their lives, and I have equal feelings about not one doctor or other purporter of a certain ideal as not being 100% right. There is much in physiology that no one has figured out. My approach is to try different things and listen to the signals my body sends me. I think it's really easy to get hung up on what one doctor says, but for me, it's about what what provides optimal health based on the way I feel.

one of my theories as to why a great majority of japanese manage to stay so slim despite eating so much and so often is that it is due to a tradition to take hot baths everyday

Although I really like my cold showers, the kind of joy is totally different from the hot shower. It is more like the nice feeling of a rigorous workout: fun, but hard at the same time.

I remember doing some research on the possible effects of cold (due to a patient of mine who has multiple sclerosis and has less musculoskeletal problems after cold water treatment). If I remember there are a lot of reasons to have some cold stress once in a while. It works a lot like physical activity, through the mechanism of hormesis.

I have not yet seen any reason why a hot shower should be avoided. Except for me, even if I don't use soap nor shampoo, hot water dries the skin (in winter).

Since mostly taking really cold showers I have improved my ability to tolerate cold. The patient I mentioned, has never been sick since she swims in cold water baths.

I would say it is worth the effort. Start with rinsing your legs with cold water at the end of your shower. See how it goes.

(fwiw, I used to be a total wuss about cold water, my younger brother and sister always made fun out of me)

I LOVE hot baths, on the odd occassion my anxiety rears it's ugly head, a hot bath with candles is sure to sort it out.

I don't know if they are unhealthy or not but nothing settles my cranky teething 4 month old better than a warm bath with mom followed by some fresh boob juice.

I long hot shower is one of the joys of life.

Just anecdotal, but I find that a hot shower before bed takes away my sleepiness. For this reason, if I'm already tired I'll use lukewarm water.

Contrast showers - after training and before bed... it's like a knockout punch.

I LOVE a hot bath, but I'm now avoiding them after intense workouts- I had read this Whole9 post on ice baths and inquired if a PWO hot bath was a bad idea, and Melissa answered that it is probably not conducive to recovery because it could increase inflammation; made sense to me. I don't have the balls yet to do a PWO ice bath, but I'm being less liberal with taking hot ones, FWIW.

http://whole9life.com/2011/04/ice-ice-baby/