An invention concerns a moisture control in a cryotherapy system and creating of snow mist. The system comprises a treatment chamber for at least one person, a closable entry to the treatment chamber, and a cooling apparatus. The cooling apparatus comprises an evaporator configured to function with a coolant and a valve for flow control of the coolant, wherein the evaporator is placed in the treatment chamber and the valve is coupled to the evaporator. The system further comprises a ventilation aperture for obtaining an additional air into the treatment chamber, the ventilation aperture being placed far from the evaporator to such spot that the additional air flows from the ventilation aperture towards the centre of the treatment chamber and simultaneously mixes with an air included in the treatment chamber so that water vapour of the additional air changes from gas to solid ice crystals and forms snow mist in the treatment chamber.
