Hyperthermia is usually applied as an adjuvant to radiotherapy or chemotherapy, to which it works as a sensitizer, in an effort to treat cancer.

[13] Before the advent of modern antiretroviral therapy extracorporeal whole body hyperthermia was tried as a treatment for HIV/AIDS, with some positive outcomes.

[10] All techniques are often combined with radiation or chemotherapy, muddying how much toxicity is the result of those treatments versus the temperature elevation achieved.

One of the challenges in thermal therapy is delivering the appropriate amount of heat to the correct part of the patient's body.

However, if the temperatures are too high, or if they are kept elevated for too long, then serious side effects, including death, can result.

The body as a whole relies mostly on simple radiation of energy to the surrounding air from the skin (50% of heat lost this way) which is augmented by convection (blood shunting) and vaporization through sweat and respiration.

To minimize damage to healthy tissue and other adverse effects, attempts are made to monitor temperatures.

Unless a needle probe can be placed with accuracy in every tumor site amenable to measurement, there is an inherent technical difficulty in how to actually reach whatever a treating center defines as an "adequate" thermal dose.

Since there is also no consensus as to what parts of the body need to be monitored (common clinically measured sites are ear drums, oral, skin, rectal, bladder, esophagus, blood probes, or even tissue needles).

Regional devices may not uniformly heat a target area, even without taking into account compensatory mechanisms of the body.

A great deal of current research focuses on how one might precisely position heat-delivery devices (catheters, microwave and ultrasound applicators, etc.)

using ultrasound or magnetic resonance imaging, as well as developing new types of nanoparticles that can more evenly distribute heat within a target tissue.

[17] During the 19th century, tumor shrinkage after a high fever due to infection had been reported in a small number of cases.

[17] A sustained high fever after induction of illness was considered critical to treatment success.

[18] Encouraging results were also reported by Warren when he treated patients with advanced cancer of various types with a combination of heat, induced with pyrogenic substance, and x-ray therapy.

[12] In locally advanced adenocarcinoma of middle and lower rectum, regional hyperthermia added to chemoradiotherapy achieved good results in terms of rate of sphincter sparing surgery.

[22] The area enclosed by the hysteresis loop represents losses, which are commonly dissipated as thermal energy.

[citation needed] Magnetic hyperthermia is defined by specific absorption rate (SAR) and it is usually expressed in watts per gram of nanoparticles.