A swimsuit (even a bikini) can reduce the positive effects of using the sauna, and also lead to an allergic skin reaction, as the artificial material from which it is made melts under the influence of high temperature. At the same time, dangerous bacteria are formed under the surface of the garment. Microbes thrive where it is warm and moist. They are also favored by damp towels and wet swimwear.
Swimsuits are mainly made of polyester. Polyester, when heated, even to body temperature, releases small plastic particles. The heat releases chemicals such as formaldehyde, perfluorochemicals (PFCs) etc., which in turn are absorbed by the skin and released to the outside. Formaldehyde is irritating to patients suffering from allergies and asthmatic conditions. In addition, according to the EU classification, it is carcinogenic. Scientists have also reported serious health issues with PFCs, linked to the risk of causing cancer. In laboratory animals, PFCs have been shown to cause damage to the liver, kidneys and reproductive system.
If we enter the sauna after swimming in the pool, in a wet suit, the chlorinated pool water evaporates from the suit and chlorine vapors get into the air. All people who stay in the sauna at that time unconsciously inhale them, and this can lead to, among other things, irritation of their skin or respiratory tract.
If we enter the pool after the sauna, the toxins from which our body has been cleansed in the sauna penetrated into the clothes, and after entering the pool or jacuzzi, they are released in the water and affect the skin of other users.
Therefore, in the guidelines of the Polish National Institute of Hygiene about using sauna it is written:
“The user should use the sauna without clothes, including a swimsuit and underwear. When bathing in a sauna, any clothing hinders the evaporation of sweat from the body surface, causing skin irritation, and in the case of synthetic fiber fabrics, the high temperature in the sauna can cause them to melt and burn the skin”.
You can find more info about proper use of sauna in sections “Rules for correct dry sauna bathing” and “Rules for correct steam sauna bathing”.