Potential Risks and Contraindications of Heat Therapy

As with all treatments, thermal (heat) therapies carry some risks and potential complications.

Potential Risks of Heat Therapy

Risks of heat application are few in number but cautionary nonetheless. There are 4 well-known consequences of incorrectly using heat therapy products and services:

• Skin rash or burn. Prolonged use of hot packs and heating pads, or application of a heat source that is overly hot without a barrier on the skin, can cause contact burns.¹Cho YS, Choi YH, Yoon C, You JS. Factors affecting the depth of burns occurring in medical institutions. Burns. 2015;41(3):604-608. doi:10.1016/j.burns.2014.09.008 A rash or burn that takes on a distinctive web-like pattern and appears red or dark is called erythema ab igne. While erythema ab igne usually fades after heat therapy is discontinued, a biopsy may be necessary to test for pre-cancerous cells.²Kettelhut EA, Traylor J, Roach JP. Erythema Ab Igne. In: StatPearls. Treasure Island (FL): StatPearls Publishing; August 10, 2020. Finally, excessive alcohol use or dehydration at a sauna may result in a loss of consciousness, which leads to serious burns that break down muscle tissue and increase the risk of kidney damage.³Koski A, Koljonen V, Vuola J. Rhabdomyolysis caused by hot air sauna burn. Burns. 2005;31(6):776-779. doi:10.1016/j.burns.2005.04.024
• Decreased blood pressure. Even after a single session of heat therapy, blood pressure will drop. Due to the sudden decrease in blood pressure, individuals who often experience orthostatic hypotension (dizziness or light-headedness upon standing) may find certain heat treatments problematic.
• Increased heart rate. The heart has to work at a faster pace to keep up with the increased blood flow to the heated area. Increased heart rate will return to baseline levels once heat treatment is removed or stopped. The changes in heart rate during and after therapy may pose significant risks for people with cardiovascular conditions such as arrhythmia.
• Increased swelling and inflammation. Heat therapy is not recommended immediately after physical activity, after injury, or during an infection. The heat will worsen pain and prolong healing if used when the tissues are damaged or infected.

Risks may be more or less worrisome at various times of year. For example, blood pressure tends to be naturally lower in the summer, so orthostatic hypotension or other cardiac events are more likely to occur in warmer weather.

Additional risks of heat therapy may exist, as this list is not comprehensive. Many of the potential risks can be mitigated, provided heat therapy is done for the suggested durations.

7 Potential Contraindications for Heat Therapy

Assessing one’s general condition is important before using the multitude of heat treatments publicly available. For example, a swollen or bruised lower back warrants an ice or cold pack to reduce the swelling, rather than a heat pack. Moderate to rigorous exercise requires a separation of at least 4 hours from use of heat therapy. In addition, certain conditions that make the skin more sensitive, such as diabetes, may preclude heat therapy – or certain types of heat therapy – as a recommended option. Consult with your healthcare provider if you have questions or concerns regarding these contraindications.

Application of heat is considered unsuitable in the presence of the following health conditions:

1. Dermatitis

Skin conditions such as contact dermatitis or eczema can be triggered by high temperatures and by low humidity, so dry heat therapy in particular can lead to flare-ups. Rashes typically fade over 2 to 3 weeks if heat therapy is stopped and dermatitis treatments are used.

2. Deep vein thrombosis

A blood clot that develops in a vein can block blood circulation back to the heart. Although a heating pad is usually suggested as part of treatment, the heat will actually increase swelling and thereby increase pain. Increased blood flow from heat therapy can also force the clot to dislodge and enter vital organs, such as the brain or the lungs, where the clot can lead to serious damage.

3. Chronic heart failure

Heart disease such as chronic heart failure impairs the body’s ability to increase blood flow and sweat in response to heat. This weakened reaction can aggravate cardiac illnesses, even including hypertension. Patients with cardiovascular problems need to gradually bring body temperature down after heat therapy. A cool shower after a sauna, for example, is better than quickly jumping into an ice bath.

4. Diabetes

High levels of heat dehydrate the body and increase blood glucose levels. Alternatively, increased blood flow from heat therapy delivers more glucose to the muscles, thereby decreasing glucose levels in the blood itself. The influence of heat on blood glucose can have significant negative consequences for patients with diabetes. However, research does indicate that global heating, such as being in a warm room, has a positive effect on the healing of diabetic ulcers.

5. Peripheral vascular disease

Sometimes known as peripheral arterial disease, this condition can be aggravated by heat. However, research suggests that frequent spa bathing may lower the resting blood pressure and may improve the ability to walk long distances.

6. Open wound

Although injuries generally benefit from heat therapy, heat used on open wounds will increase blood flow to the wound and potentially increase bleeding.

7. Severe cognitive impairment

Dementia can interfere with remembering to turn off a heat product or remembering how long it has been since walking into a sauna. It is also important to note that heat therapy is not always compatible with alcohol consumption, which has led to rare occurrences of death when using the sauna.

Patients with any of these conditions can further discuss the risk of moderate forms of heat therapy, as well as safer alternatives, with a doctor.