Positive medicine - sauna, steam rooms and cold dips

Sweatfest

My best sauna and steam experiences have been up in Gazelle resort in western Turkey (near Lake Abant), seven different saunas from hot and hotter to salt, farmyard-acoustic (!) to the Turkish hammam.  I also used to exchange with a German lad as a boy whose family would have a weekly outing to one.  So what's the medical effect of these saunas?

Sauna and steam room
What is a sauna, what'a a steam room?
Finnish sauna: dry heat, 15-30% humidity, 80-90 centigrade.  2-3 heat-cool cycles each of 15 mins+.  The Finnish are the cultural custodians of the sauna - having one in almost every home  LINK (1997)
Turkish bath / steam room: 100% humidity at 41 centigrade.  Limited research available on these.

Cardiovascular effects of sauna: 

• Equivalent stress to the system as a brisk walk LINK (1997), p. 656 
• Saunas significantly reduce the risk of cardiovascular disease and all-cause mortality LINK (2015)
• Orthostatic hypotension possible in those on antihypertensive medication, generally acceptable in cardiovascular diseased patients unless their hypertension is poorly controlled. LINK (1997), p. 657 

Respiratory effects of sauna:

• Absenteeism reduction: in children taking a once weekly sauna in two studies, and replicated in a study with an adult group after 3 months, absenteeism caused by URTI was reduced by 50% LINK (1997).  However, one study did not replicate this LINK (1994)
• Chronic/recurrent sinus symptoms: no effect of steam inhalation LINK (2016)
• Bacteria: few micro-organisms are viable above 80 degrees so sauna air is relatively sterile and risk of inhalation of active microbes is small LINK (1997), p. 656 
• Heat: in sauna, water and heat transfer to the lung tissue remains small, and hence negligible risk of thermal-induced lung damage.  LINK (1997), p. 656 

Effects of sauna on skin: LINK (2008)

• Improved epidermal blood perfusion  (by 20-40x) during LINK (1997), p. 656 and with a preserved effect after regular saunas LINK (2008) 
• Improved water-holding capacity of skin (i.e. less dry skin) and recovery of skin pH, both of which are associated with stability of the epidermal barrier and prevention of skin disease LINK (2008)  
• Unclear effects on skin turgor

Cold water immersion 
The icy plunge pool after that delightfully relaxing hot room...

• Reduces dehydration from sweat after sauna (due to more rapid cooling) and transiently induces skin oedema, thereby smoothing those wrinkles temporarily!  LINK (1997), p.655
• Cold exposure activates deposits of brown fat - which are metabolically active.  Frequent exposure to cold increases the activity of these which encourages weight loss LINK (2012) ; LINK (2014)
• Cochrane reviews have found no consistent evidence that cold dips reduce muscle soreness LINK (2015)
• It's certainly invigorating, whether after a sauna or in a wetsuit on a cold day.  Gets easier the longer you stay in.  Mechanism likely is through plasma noradrenaline, adrenaline, cortisol and endorphins LINK (1997), p. 655

Summary
Saunas seem to be much the equivalent of exercise - positive respiratory and cardiovascular effects, and a healthy glow.  Just sociably and in the calm!  As for the cold dips, well, that's just more hardcore, isn't it?!

Brass monkeys