||This article needs additional citations for verification. (March 2012)|
Heat therapy, also called thermotherapy, is the application of heat to the body for pain relief and health. It can take the form of a hot cloth, hot water, ultrasound, heating pad, hydrocollator packs, whirlpool baths, cordless FIR heat therapy wrap, and many others. It can be beneficial to those with arthritis and stiff muscles and injuries to the deep tissue of the skin. Heat may be an effective self-care treatment for conditions like rheumatoid arthritis.
Heat therapy is most commonly used for rehabilitation purposes. The therapeutic effects of heat include increasing the extensibility of collagen tissues; decreasing joint stiffness; reducing pain; relieving muscle spasms; reducing inflammation, edema, and aids in the post acute phase of healing; and increasing blood flow. The increased blood flow to the affected area provides proteins, nutrients, and oxygen for better healing.
- Direct contact
Moist heat therapy has been believed to be more effective at warming tissues than dry heat, because water transfers heat more quickly than air. Clinical studies do not support the popular belief that moist heat is more effective then dry heat. Moist heat results in the perception that the tissue is heated more deeply. In fact, recent studies indicate that vasodilation, the expansion of the blood capillaries (vessels) to allow more blood flow, is improved with dry heat therapy. Expansion of the blood capillaries is the primary objective of heat therapy. A recent study clearly concluded the positive results of dry heat therapy versus moist heat therapy. Heat therapy increases the effect on muscles, joints, and soft tissue. Heat is typically applied by placing a warming device on the relevant body part.
Newer breeds of heat therapy devices combine a carbon fiber heater with a cordless rechargeable lithium battery and are built into the specific body wrap (i.e., shoulder wrap or back wrap) for targeted heat therapy. Such devices can be used as alternatives to chemical or plugged-in heating pads, but have not been shown to improve the clinical benefit. All devices primarily provide heat to promote vasodilation.
- Infrared radiation
Infrared radiation is a convenient system to heat parts of our body. It has the advantage over direct contact in that radiation can heat directly the area where the blood capillaries and neuron terminals are. When heat comes from a direct contact source it has to heat the external layer of the skin, and heat is transferred to the deeper layer by conduction. Since heat conduction needs a temperature gradient to proceed, and there is a maximum temperature that can be safely used (around 42°C), this means lower temperature where warming is needed.
IR-A, from 0.78 to 1.4 μm.
IR-B, from 1.4 to 3 μm.
IR-C, from 3 μm to 1 mm.
IR radiation is more useful than the visible radiation for heating our body, because we absorb most of it, compared to a strong reflection of visible light. Penetration depth of infrared radiation in our skin is dependent of wavelength. IR-A is the most penetrating, and reaches some millimeters, IR-B penetrates into the dermis (about 1 mm), and IR-C is mostly absorbed in the external layer of the epidermis (estratum corneum). For this reason the infrared lamps used for therapeutic purposes produce mainly IR-A radiation.
Mechanism of action, and indications 
Because heat is a vasodilator, it should be avoided in tissues with inadequate vascular supply, in case of acute injury, in bleeding disorders (because heat would increase bleeding), in tissues with a severe lack of sensitivity, in scars.
Another use is the treatment of infection and cancers by the use of heat. Cancer cells and many bacteria have poor mechanisms for adapting to and resisting the physiological stresses of heat, and are more vulnerable to heat-induced death than normal cells.
For headaches 
Heat therapy can be used for the treatment of headaches and migraines. Many people who suffer from chronic headaches also suffer from tight muscles in their neck and upper back. The application of constant heat to the back/upper back area can help to release the tension associated with headache pain. In order to achieve heat therapy for headaches, many use microwaveable pads which can often overheat, potentially leading to injury, and lose their heat after a few minutes. Some new products use heated water, running through pads, to maintain a constant temperature, allowing headache sufferers to use hands-free heat therapy in the treatment of their headache pain.
In plants 
Thermotherapy may also be used in vine propagation to get rid of viroids (particles smaller than viruses) which may affect the new vine.
See also 
- Infrared radiation, one means for delivering heat
- Migraine#Cryotherapy and Thermotherapy
- TDP lamp
- Thermotherapy for treating rheumatoid arthritis, from Cochrane Library
- Prentice, William E. Arnheim’s Principles of Athletic Training: a Competency Based Approach. New York. McGraw-Hill. 2008.
- "The Impact of Dry Versus Moist Heat", Regina M. Fink, RN, PhD, AOCN, 9/8/2009, Oncol Nurs Forum
- The International Commission on Non-Ionizing Radiation Protection (ICNIRP). "ICNIRP Statement on Far Infrared Radiation Protection". Health Physics Society. Retrieved 2011-02-12.
- Raj, P. Pritvi, Practical Management of Pain. Mosby. 2.000. ISBN 978-0-8151-2569-3.
- Israel, Beth. “Pain”. Stoppain.org. 2005. Date Assessed: 28 April 2009. 
- "Deep Heat Treatment.." CRS - Adult Health Advisor (Jan. 2009): 1-1. Health Source - Consumer Edition. EBSCO. Kent Library, Cape Girardeau, MO. 30 Apr. 2009 
- Scott F. Nadler, DO, FACSM, Kurt Weingand, PhD, DVM, and Roger J. Kruse, MD. “The Physiologic Basis and Clinical Applications of Cryotherapy and Thermotherapy for the Pain Practitioner”. Pain Physician. 7 (2004): 395-399.