There is a growing interest in the use of thermal interventions to improve both physical and mental health. The premise being that a perturbation of the homeostatic system through thermal challenges will provoke some of the adaptations seen with exercise. This is very promising as it has the potential to impact groups who are unable or unwilling to exercise. However, like exercise, thermal interventions are not without risk and with widening participation the risks may not always outweigh the benefits. This discussion will consider the risks associated with cold interventions.

Cold water dipping or swimming is increasingly popular and will invoke a powerful sympathetic response on entry into the cold water. These initial responses, often called the cold shock response, are driven by a rapid fall in skin temperature and evoke an inspiratory gasp, uncontrollable hyperventilation, inspiratory shift, tachycardia and hypertension. The dyspnoea associated with the respiratory responses reduces breath hold time and can induce panic which may result in swim failure. Arrhythmias may also occur during this period particularly if there is intermittent submersion and breath-holding. In individuals with underlying cardiovascular issues, a population who may consider thermal interventions over exercise, this increased workload of the heart may result in a cardiovascular or cerebrovascular accident. These risks can be mitigated by careful health screening, reducing the rate of skin cooling (warmer water, slow entry, wetsuits) until the individual is habituated and by providing a safe swimming environment with easy egress points.

Nerve and muscle function are impaired with cooling and therefore as the duration of immersion increases swimming performance will be impaired, potentially to the point of swim failure. The decreased tactile sensation and impaired muscle function may also impair the ability to egress the water especially if balance and coordination are required (e.g. with wave action and rocks). Immersions longer than 30 minutes may cause hypothermia with the consequent decline in both physical and cognitive function. Even in the absence of hypothermia, cold water swimming can trigger transient global amnesia. Consideration should also be given to the continued fall in deep body temperature after getting out of the water and the consequent effects on driving performance if adequate and appropriate rewarming is not undertaken. Rewarming in a hot sauna could pose a further risk due to increased vascular strain in a hypovolemic individual.

Prolonged or repeated exposure to cold may aggravate Raynaud’s Phenomenon symptoms and potentially cause non-freezing cold injury (NFCI) particularly in the extremities where intense vasoconstriction will occur. The dose of cold (duration and temperature) that causes NFCI is not known, though it is likely that the longer the hands and feet are cold (both during immersion and before complete rewarming) the greater the risk. All of the above risks will be exacerbated in ice baths as the rate of cooling and consequent magnitude of response will be greater.

Therefore, whilst thermal interventions are emerging as a potential exercise mimetic, like any medicine, they are not without side effects.