Superficial Heat and Cold Technique

Updated: Dec 13, 2022
  • Author: Milton J Klein, DO, MBA; Chief Editor: Dean H Hommer, MD  more...
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Conductive Heating

Conductive heating is usually a simple modality that can be taught to the patient for independent home use. The disadvantages of this modality include the following:

  • Potential burns
  • Difficulty with its application to regions exhibiting abnormalities (eg, the foot)
  • Skin-drying effect (with the exception of paraffin and water media)

Another complication that may occur is impairment of local vascular supply, due to the weight of the modality on the limb or the weight of the limb on the modality. This phenomenon also may be caused by an uneven distribution of pressure on the anatomical region that the medium contacts.

Hot packs

Hot packs or hydrocollator packs contain silicate gel in a cotton bag. These packs are placed in a hot water tank, which is thermostatically controlled at 71.1-79.4°C. The silicate gel absorbs a large quantity of water and has a high heat capacity.

Hot packs are applied over layers of towels for 20-30 minutes. Most of the heat transfer from the hot pack to the patient is by conduction. Increasing the towel thickness reduces the heat flow and produces an intentional slowing in the temperature rise. Acceleration of heat transfer occurs if the hot pack leaks into the towel. The patient never should lie on the hot pack, as the body weight could squeeze hot water out of the pack into the towel and potentially cause a burn.

The maximum skin temperature is obtained after 8 minutes, followed by a reduction in temperature due to increased blood flow. Repeated application of hot packs may prolong the period of temperature elevation but does not alter the temperature distribution.

Other forms of hot packs include Kenny packs (vigorous, short-term stimulation/heating), rubber hot water bottles, and electric heating pads. Heat transfer is enhanced if the pad is moist or if the heated part is wrapped in moist material. Complications that can arise from using an electric heating pad include shock hazard if the device is not insulated properly and burns if the patient falls asleep lying on the pad. Heat output increases over time until equilibrium is achieved. Keep in mind that heat may be sufficiently analgesic to produce burns.

Indications for the application of hot packs may include painful muscle spasms, abdominal muscle cramping, and menstrual cramps. Hospitalized patients receive circulated warm-fluid hot packs to minimize the potential for burns due to prolonged superficial heating application, a particular concern in sensory impaired or mentally challenged patients. Chemical packs often are available in containers that, when properly manipulated, allow previously separated ingredients to mix, thereby producing an exothermic chemical reaction that causes heat production.

Paraffin bath

A paraffin bath is another form of conductive heating. Paraffin baths are particularly useful for contractures due to rheumatoid arthritisburns, and progressive systemic sclerosis (scleroderma). Paraffin usually is applied to the hands, arms, and feet. Paraffin wax is melted and mixed with liquid paraffin. For therapeutic use, the paraffin bath is maintained at the melting point of 51.7-54.4°C in an insulated, thermostatically controlled container. The two application methods are (1) the dip method and (2) immersion.

In the dip method, the hand or foot is placed in the liquid paraffin bath and withdrawn when a thin layer of warm, solid paraffin forms, becomes adherent, and covers the skin. The dipping procedure is repeated until a thick paraffin glove is formed. The heat can be retained by wrapping with towels for 20 minutes; then, the cool, solid paraffin glove is peeled away and the paraffin is recycled. The dip method is a mild heat application because only a limited amount of heat is available for transfer to the skin

In the immersion method, the body part is immersed in the paraffin bath for 20-30 minutes. The immersion method transfers heat not only from the solid paraffin block but also from the liquid paraffin bath itself. The heat transfer rate from the liquid paraffin bath to the skin is slowed as the solid paraffin glove provides a poor thermal conductor. This modality represents a vigorous heat application, causing a significant increase in skin tissue temperature, up to 46°C, with a marked temperature decrease in the subcutaneous tissue. Water at the same temperature applied by the same method would be intolerable because of the high specific heat and thermal conductivity.


Convective Heating

Fluidotherapy is a form of convective heating that uses a bed of round, uniform, finely divided solids, such as glass beads, into which thermostatically controlled warm air is blown to generate a warm, semifluid mixture. Part of the patient's hand, foot, or limb can be immersed for superficial heating. This technique applies dry heat, and the temperature is equivalent to the hot air that is blown into the bed of beads. The usual treatment temperature range is 45.6-47.8ºC.

Hydrotherapy (see the image below) can include total immersion in a large hot tub or Hubbard tank. [19]  Whirlpool baths can be used for partial immersion of the upper or lower extremities. Because hydrotherapy also may be used in treating infected draining wounds, the equipment must be sterilized between uses.

Hydrotherapy. Image courtesy of Wikimedia Hydrotherapy. Image courtesy of Wikimedia

The water is agitated, and the size of the tank determines the capacity (the entire body or just the upper or lower extremities). For total body immersion in water, the temperature should not exceed 40.6ºC. Partial immersion of a limb should have a maximum temperature of 46.1ºC. The treatment time is limited to 20-30 minutes each session.

As a precaution during total immersion of a patient in water temperatures over 37.8ºC, his/her oral temperature should be observed to prevent a rise of body core temperature. With total body immersion, heat loss occurs primarily through the head and neck; therefore, the heat regulatory mechanism is impaired significantly. Total body immersion has a relaxing effect and may predispose the patient to hypotension due to peripheral blood pooling (secondary to vasodilatation of all four limbs).

Contrast baths provide a method of therapeutic hyperemia for management of rheumatoid arthritis or sympathetically mediated pain (eg, rheumatoid arthritis of distal joints, hands, feet; prolonged ankle swelling after an ankle sprain/strain in refractory joint effusions). A differential of approximately 25°C exists between the hot and cold water. The hot water is at a temperature of 40.6-43.3°C. The cold water temperature is maintained at 15-20°C.

The greatest hyperemia response is produced by hot water immersion for 10 minutes followed by cold water for 1 minute. The cycle continues with hot water immersion for 4 minutes and cold water for 1 minute; this 4:1 cycle is repeated for a total of 30 minutes at each physical therapy appointment or during each home-based self-treatment session. Other approaches to convective heating include water-based exercise and spa therapy (balneotherapy). [20]

Another convection modality is the moist air cabinet. Air saturated with water vapor at a controlled temperature is blown over the patient, causing superficial heating over a large area. The temperature distribution in this modality provides heating of skin and superficial tissue. This modality is used most commonly for back muscle spasms and polyarticular arthritic conditions. The recommended temperature maximum is 40.6ºC.


Conversion Heating

Radiant heat therapy is a type of conversion heating; high-energy photons penetrate the tissues, and this energy is converted into heat. Because photons of longer wavelengths process less energy, penetration is more superficial; shorter wavelengths have a greater therapeutic benefit. The therapeutic, radiant heat–producing temperature rise in tissues ranges from the spectrum of far infrared to visible yellow. Longer wavelengths of light, from green to ultraviolet, produce photochemical reactions that do not significantly raise tissue temperature.

Most other commercially available radiant light sources produce infrared with some visible light. These lamps contain heating elements of silicon carbide, special quartz tubes, or metal alloys. The higher-energy photons are produced by shorter-wavelength radiant heat, resulting in a greater penetration of superficial tissue.

A treatment time of 20-30 minutes is recommended, with the maximum effect occurring at a minimum of 20 minutes. The radiant energy source is positioned 15-24 in. (38.1-61 cm) from the treatment site. The intensity is controlled by the light source, distance, type/quality of reflector, and air movement. With heat lamps, guidance concerning treatment time is given by the patient's subjective feeling of warmth. The conventional single heat cradle with an output of 300 W is not likely to increase body temperature; however, a double cradle could. Patients also could receive increased radiation after an hour of treatment time.

Infrared radiation can be used for reflex vasodilatation where vasospasm is present. Because of the photochemical effect of lower-energy, ultraviolet photons, this radiant energy is used most effectively for the treatment of psoriasis and other dermatologic conditions.



Immediate application of ice or cold packs for superficial burns and for burns on less than 20% of the total body surface area decreases pain, edema, erythema, and blistering. For optimal results in cases of trauma, cold should be applied before significant edema and hemorrhage occur.

The most common methods of cold application include cold packs, cold immersion, ice massage, and cooling during exercise (cryokinetics). The treatment known as spray and stretch consists of an application of cryotherapy with a vapocoolant spray (see the image below), which then is followed by stretching of the involved muscles. This technique sometimes is used in the management of myofascial pain syndromes, as described by Travell and Simons. [21]

Schematic drawing showing how the jet stream of va Schematic drawing showing how the jet stream of vapocoolant is applied.

Therapeutic cold is applied for 5-20 minutes, followed by a rest period of 30 minutes. For the treatment of acute sprains/strains and postoperative care, application of cold is recommended for the first 24-48 hours.

For the treatment of deeper tissues or for prolonged periods of cold application, physician evaluation/prescription is essential to avoid complications. The most useful local therapeutic cold applications include for the management of edema, muscle spasm, bleeding, and traumatic pain. The vasoconstrictive effect of therapeutic cold is beneficial for reducing posttraumatic swelling and pain, as well as for reducing hemorrhage into soft tissues.



Complications of conductive heating may include the following:

  • Potential burns
  • Skin-drying effect (except with paraffin and water media)
  • Impairment of local vascular supply

Convective heating in the form of hydrotherapy can predispose the patient to hypotension due to peripheral blood pooling.

Conversion heating can raise patient body temperature (if heat lamp treatment time is not monitored).