What Is Heat Therapy?

Introduction

Heat therapy, a technique that has been used for thousands of years, is the application of a heat source to the body to raise the temperature of that area. This can serve many purposes, including pain relief, particularly muscle soreness following exercise, and enhanced healing after injuries. These effects of heat therapy result from the ability of heat to alter several processes in the body, primarily increasing blood flow and reducing inflammation. Ultimately, several different techniques can be used to deliver heat therapy, with these being categorised as dry or moist, depending on whether they involve the use of water. Different types of heat therapy may be more suitable for different types of conditions and can carry various risks and benefits.^1,2

Types of heat therapy

Broadly, heat therapy can be divided into two types, dry and moist, depending on whether water is being used. Dry types of heat therapy can include hot packs, heating pads, and warm towels, whereas wet types of heat therapy can include warm baths or showers, hot water bottles, and warm compresses.^1,3

How does heat therapy work?

Increased blood flow

Heat causes the blood vessels to widen, a process known as vasodilation. This heat-induced vasodilation occurs as the body aims to redirect blood flow to the surface of the skin, where it can be released. Increasing blood flow allows the body’s tissue to receive more nutrients and oxygen.^4,5

Muscle relaxation

Through several biochemical processes, heat regulates the expression of several proteins. One of these proteins is heat stress protein 70, which is increasingly expressed in response to heat, which stabilises the structure and function of muscle, preventing it from wasting. Heat also reduces the expression of a protein called MAFbx to further prevent the wasting of muscle. Heat therapy can increase blood flow to muscles, providing them with more nutrients and oxygen, and can reduce stress to muscles, allowing muscle to be less inflamed, tolerate stress better, gain mass, and have enhanced function.⁶

Pain relief

As heat therapy causes vasodilation and improves blood circulation, can increase the ability of the tissue to extend, and can reduce the stiffness of joints, it ultimately is able to provide pain relief.⁷

Indications for heat therapy

1. Muscle cramps and muscle pain: Muscle cramps cause muscle pain and are temporary, intensely painful contractions of muscle. Muscle pain can be localised or widespread and be short-lasting or long-lasting. Muscle cramps and muscle pain tend to be paired with muscle weakness and difficulty moving.^3,8,9
2. Arthritis and joint stiffness: Arthritis is characterised by swelling and stiffness of joints which results in pain. There are various types of arthritis, including rheumatoid arthritis, osteoarthritis, autoimmune arthritis, psoriatic arthritis, and reactive arthritis.^10,11,12
3. Back pain: Back pain can result from various causes and is a widespread condition that can have short-term and long-term effects and vary in severity. Nearly one in four adults have chronic back pain. Back pain can make moving, and therefore going about your day-to-day activities, challenging.^13,14
4. Menstrual cramps: During a period, some people will experience abdominal cramps. This can impact the lower abdomen but can also impact the back of the legs. Menstrual cramps can be paired with nausea, vomiting, diarrhoea, and headaches.^15,16
5. Sports injuries: Athletes are at a particular risk for physical trauma. This trauma can occur as a result of events like falling over or overusing the muscles.^17,18

Safety precautions and considerations when using heat therapy

Though heat therapy can be an effective treatment for a range of conditions, it is important to take several precautions and considerations when using it:^2,19

• Don’t apply heat therapy 24 to 48 hours after a sudden injury
• Don’t apply therapy to open or damaged skin
• Heating pads should be placed in a pillowcase or towel before being placed on the skin
• Remove the heat-therapy device from the skin after two to three minutes if there’s redness and pain
• Don’t use heat therapy if your temperature is raised
• Take precautions if you have an inflammatory condition, such as cancer, multiple sclerosis, or osteoarthritis, as heat therapy can worsen inflammatory conditions 

FAQs

What are the different types of heat therapy?

The different types of heat therapy can be divided into two categories, dry and moist, depending on whether water is being used.¹ Hot packs, heating pads, and warm towels are forms of dry heat therapy and warm baths or showers, hot water bottles, and warm compresses are forms of moist heat therapy.

What conditions can be treated with heat therapy?

Numerous conditions can be treated with heat therapy, including muscle cramps and muscle pain, arthritis and joint stiffness, back pain, menstrual cramps, and sports injuries.^{3,11,12,14,16,18}

How long and how often should I apply heat therapy?

The duration of heat therapy can vary depending on the type of heat therapy and the condition for which the heat therapy is being used, though it can range from five to 20 minutes.^{20 21}

What temperature should the heat be set at for effective heat therapy?

The temperature of heat therapy typically is in the range of 35 to 40 degrees Celsius.²¹

Does heat therapy carry any risks?

Heat therapy does carry several risks, particularly when involving higher temperatures, including burns and skin ulcerations. Furthermore, heat therapy can worsen inflammatory conditions, such as cancer, multiple sclerosis, and osteoarthritis.²

Are there any medical conditions where heat therapy should be avoided?

Heat therapy should not be applied to open or damaged skin or in conditions that cause such. With inflammatory conditions, heat therapy should be used with caution as it can worsen these.^{2 19}

Is heat therapy suitable in pregnancy or in children?

Heat therapy can be used for pregnant women and children, though it is particularly important to take precautions to ensure it is as safe as possible.^{22 23}

Can heat therapy help with muscle soreness after exercise?

Heat therapy can be used to help relieve muscle soreness after exercise.¹

Summary

Heat therapy is the application of a heat source to the body to increase the temperature of the area of the body to which it is being applied. The temperature of the body is increased, blood flow is boosted, and inflammation is reduced, which in turn promotes pain relief and healing. Ways in which heat therapy can be applied vary but can broadly be classified as dry or moist, with dry types including hot packs, heating pads, and warm towels and wet types including warm baths or showers, hot water bottles, and warm compresses. The numerous forms of heat therapy can be useful to help treat several conditions, including muscle pain and spasms, arthritis and joint stiffness, back pain, menstrual cramps, and sports injuries, making it a very versatile treatment.