Thermolysis describes the use of heat to break down substances (thermo meaning temperature and lysis meaning breakdown or destruction). This is often accomplished by immersing the affected area in hot water.
Proteins are essential organic compounds that perform a vast array of functions within living organisms. Most life forms live in temperatures below 122°F (50°C). Above this temperature, their proteins will suffer an irreversible unfolding of their three-dimensional biomolecular structure. This process has damaging consequences to their function and is called protein denaturation.
Application of heat may denature venoms that are comprised of proteins, thus eliminating their effect or reducing their potency.
The standard recommendations for toxin denaturation as a first-aid measure call for immersing the affected area in hot freshwater with an upper limit of 113°F (45°C) for 30 to 90 minutes. This may work reasonably well when the toxin inoculation is skin deep, such as with a jellyfish sting, but will be less effective when toxins have been inoculated by means of deeper puncture wounds, as is the case of lionfish spines. Though quick reasoning could call for increasing the temperature, applying higher temperatures at skin level in an attempt to reach the desired temperature at a deeper level poses an unacceptable risk of burning the skin. In addition, vasodilatation caused by exposure to elevated temperatures may expedite the onset of absorption and of systemic effects.
Each case is unique and requires some estimation of the depth to which the venom was injected; for superficial inoculations, application of heat might be useful to manage pain and denature toxins, whereas for deeper inoculations, heat is for pain management only.
If you attempt to use thermolysis as a first-aid measure, minimize the risk of local tissue damage to the injured diver by testing the water on yourself first on the same area where the diver is injured. Use the hottest temperatures you can tolerate and avoid scalding. Do not rely on the victim's assessment, as intense pain may impair his ability to evaluate temperature tolerability.