Cryotherapy Safety Oftentimes, in treating injuries a cold pack is immediately applied to the skin of the affected area. Penetration of the cooling effect to the underlying target tissue is essential to derive the desired therapeutic benefit. A major concern relating to using the pack is that it should be cold enough to produce a therapeutic effect and not be so cold as to cause thermal injury of the skin at the site of application. If the surface temperature of the skin should not be lowered to less than 5°C, how cold can the pack be pre-cooled safely? Also, what will be the rate of heat transfer from the skin to the cold pack during the first 10 min of treatment? The gel within a typical cold pack consists of a solution of water and salt (to reduce the freezing temperature) with a small amount of cellulose added to increase the viscosity. The eutectic temperature for a sodium chloride (23.3% by weight) and water mix- ture is –21.2°C.