What heats deeper, Finnish or infrared?

This is a response to a great comment by Klaus on my post from the early days of this blog, about the difference between the infrared sauna and the traditional Finnish sauna. This response started as a follow-up comment, but I decided to make it a blog post later, because it covers an interesting topic of sauna heat and how “deep” it heats.

Klaus,
First, I want to thank you for this extensive explanation of principles behind the traditional Finnish sauna. Indeed, the key qualities of the traditional sauna are low humidity combined with high temperature. With higher humidity you’ll get the hammam (the Turkish bath) or the Russian banya. There is also a spa product, steam bath, which uses a lot of steam.

Now about ‘an infrared sauna heats you more deeply than steam sauna’ statement. It was my opinion back in 2005, when this post was written, I had less knowledge about both infrared and traditional saunas. Now, I know more and it makes sense to explain my current view.

Does the infrared sauna heat you deeper than the traditional one? As I think now, this question is not correct. What is “deeper”? Is 2 °C increase in core temperature “deeper” than 1 °C increase? Both saunas increase core temperature, depending on session length.

Depth of the layer of superficial tissues which has higher than core temperature can be taken as a measure of penetration. But this depth is mainly a function of thermoregulatory response or a human body and the total heat coming from outside. There is no difference if heat comes from infrared heaters or from extremely hot sauna air.

More than that, the Finnish sauna takes only about 10 minutes to increase the body temperature by 1 C, while the typical infrared sauna needs about 30 minutes for that. To me it means than the traditional sauna provides more heat to a body in a given period of time. Someone may argue that the infrared one can rise core temperature more than 1 C, which is unlikely, not only because there is no hard data supporting this claim (for the common infrared cabins, not for the medical devices for causing hyperthermia), but also because the common practice for the traditional sauna is to cool down after 10 minutes. More than 1 °C increase in core temperature is not advised both for the infrared and traditional saunas.

I see the difference between these saunas in the way they act. The traditional sauna is like a shock for a body. It gives a quick rise in temperature, and body should respond immediately with sweating and increased circulation.

In the infrared sauna, temperature increase occurs more gradually. There is no need for a quick thermoregulatory response. As a side effect, you can lose more sweat in the infrared cabin, because you spend there 30 minutes instead of 10 (on average). It doesn’t mean, however, that you will sweat three times more.

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