Hot Applications

Hot Applications (Thermotherapy): Overview

Alternative names: Thermotherapy, heat therapy.

Thermotherapy is the use of heat to treat symptoms of acute or chronic pain, especially those related to muscle tension or spasm.  It is also a common treatment for arthritis, bursitis, tendonitis, back pain, shoulder pain and other kinds of joint pain.

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Hot applications result in an increase in molecular vibration and cellular metabolic rate.  This form of treatment is divided into two categories, namely superficial and deep heating modalities.  These are further divided into chemical, electric, or magnetic.  Temperatures range from 105 to 170 degrees Fahrenheit (41°C to 77°C).  Superficial modalities include infrared lamps, moist heat packs, paraffin baths, and warm whirlpools.  Deep heating modalities include microwave diathermy, shortwave diathermy, and ultrasound.  The body reacts with a series of local and systemic effects.

People often apply heat therapy at home for minor conditions.  It is also used in healthcare settings, such as physical therapy, manipulation therapy and occupational therapy.

Function; Why it is Recommended

Whereas cold therapy produces blood vessel constriction in localized tissues to decrease swelling and relax skeletal muscles, heat therapy facilitates the healing process by producing blood vessel dilation, thereby enhancing local blood flow decreasing edema, increasing tissue temperature and producing pain relief.

Thermotherapy widens blood vessels and increases blood flow to the skin.  It relaxes superficial muscles, decreases muscle spasms and reduces stiffness of joints.  Research has shown that it can also block pain receptors.

Moist heat appears to be more effective in treating pain than dry heat, as the moisture allows the heat to penetrate more deeply into the muscle.  Thermotherapy is frequently used combination with other therapies to relieve pain, such as hydrotherapy (water therapy).  In many cases, cryotherapy (cold therapy) is used to reduce inflammation before thermotherapy is used to increase blood flow to muscles.

There are several methods of delivering thermotherapy to the body.  They include heating pads and:

Heat Creams and Ointments
These popular over-the-counter remedies can provide relief from minor muscle pain.  However, these topical treatments do not penetrate very deeply into muscle tissue, making them less effective in treating more significant pain.

Warm Compresses and Hot Packs
Moist heat packs are made of silica gel and are considered a superficial heating modality.  Heat packs are fairly convenient and are kept in a hydroculator.  Larger heat packs should be used for areas such as the low back or quadriceps, while the smaller, longer ones should be used for the cervical area.  The temperature should range from 145-170°F. These packs should be used for 15-20 minutes, and be placed in a cloth pad to protect from burns.  Additional towels may be necessary.  The patient should try to avoid lying on the heat pack, and should be in a comfortable position.

Hot packs are heated, cloth-covered pouches with a core of silica gel.  They provide relief of pain located in a patient's trunk, spine or limbs.  Hot packs also are used to treat muscle spasms, and the inflammations of tendonitis and bursitis.  Variations of this type of therapy include hot water bottles, warm and moist compresses and electric heating pads.

Paraffin Bath
Paraffin (waxy white or colorless solid hydrocarbon mixture used to make lubricants) is mixed with mineral oil in a special basin into which the affected limb is immersed.  This treatment can provide relief of arthritic symptoms.  These units can also be bought for use at home.

Paraffin dips use a mixture of oil and water to heat an area usually irregular in shape and somewhat small, such as a hand.  The temperature ranges from 118 to 126°F. It is fairly inexpensive but not too convenient.  Paraffin baths are generally used for arthritis and other chronic inflammatory conditions.  There are two common methods for use:

  • Immersion Bath: The patient dips the body part in the wax and removes it so that it dries, then re-dips 6-12 times while allowing it to dry between dips.  Then the patient immerses the body part for 5-10 minutes, with care being taken to avoid burning.
  • Pack Glove Method: This method is safer than the immersion bath because there is less chance of burning.  With this, the patient dips the body part in the wax and lets it dry.  This is repeated 7-12 times.  After the last dip, the body part is covered with a plastic bag and then a heat pack is placed over the injury to keep it in the heat.

Warm Whirlpool Baths
Like the cold whirlpool, it is expensive and inconvenient to use a warm whirlpool.  Despite this, it is good for covering large, irregular surface areas.  The temperature should range from 105 to 110°F, and the duration of treatment should last from 15 to 20 minutes.  If the core body temperature gets too high, hyperthermia should become a concern.  Whirlpool baths promote vasodilation and help stretch collagen tissue.

Ultrasound Therapy
A method of applying deep heat to tissues using high-frequency sound waves.  Transmission gel, oil or water is applied to the skin covering certain areas of the body.  Energy derived from a quartz crystal is then the passed from an applicator through the gel, creating deep heating to soft tissue and bone that increases blood flow and tissue metabolism and raises a patient's pain threshold.

Ultrasound is a form of acoustic energy utilized for its thermal and non-thermal effects.  To deliver these acoustic waves, there is an instrument with a metal faceplate containing quartz crystals inside.  When mechanically altered, they produce an electric output.  Therapeutic ultrasound has been used to stimulate the repair of soft tissue injuries and to relieve pain.

For thermal effects to occur, energy must be absorbed.  One wants to attain a deep penetration of the heat, with the optimum depth of penetration being 3-5cm (as opposed to a heat pack, which heats only 2cm deep).  Non-thermal effects include micromassage (microscopic movement of fluids and tissues), which leads to an increase in membrane permeability and arterial vasodilation and constriction.  The indications for thermal and non-thermal ultrasound are quite different, but the precautions are the same.  Avoid:

  • Areas with decreased sensation and circulation
  • Eyes, esophagus, reproductive areas
  • Using during pregnancy
  • On cancer patients
  • On those with a cardiac pacemaker.

Clinical applications of therapeutic ultrasound include:

  • Inflammation: Acute and subacute phases

    • Utilized at low intensities to promote absorption of proteins
    • Decreased risk of poor structural formation of collagen (scar tissue)
  • Pain and Nerve Conduction:

    • Ultrasound selectively heats peripheral nerves, and alters or blocks impulse conduction and increases membrane permeability
    • May block pain mechanism through effecting nerve
  • Circulation:

    • Improved local circulation.

The heating effect occurs when the ultrasound is on continuously.  For non-thermal effects, one should be aware of the duty cycle, which represents the on and off time of the ultrasound.  In the case of pulsed ultrasound, the duty cycle may be 20%, 40%, 50%, etc.  In the case of 20% duty cycle, the ultrasound is only on 20% of the time.  For acute injuries, the setting should be 20-50%.  For subacute injuries, the duty cycle should be 50-80% to aid in the change-over to heating modalities.

For both thermal and non-thermal ultrasound, the following are appropriate intensities: acute – 0.1-0.5 watts/cm2, subacute – 0.5-1.0 watts/cm2, chronic – 1.0-1.5 watts/cm2.  All treatments should last 5 minutes.

When applying therapeutic ultrasound, a transmission gel should be used to produce better conductivity.  It is important to use a small, circular pattern while keeping the ultrasound head in constant contact with the area.  This maintains a high coupling effect, which will allow the patient to receive the greatest benefits.

Ultrasound can also be transmitted through water in cases where the area being treated is irregular in shape or the faceplate is too large to accommodate the area.  The patient sticks the area in a bucket of water while the therapist holds the faceplate just under the surface of the water, 2 inches above the area being treated.  An important point to keep in mind is that 60% of the ultrasound intensity is lost through water.  So the intensity level needs to be increased to account for this.

When turning the ultrasound on, the ultrasound head must be kept in contact with the gel or water.  This helps prevent the crystals inside the head from shattering.

This is a treatment using microwaves or shortwaves which are selectively absorbed by tissues with high water content.  Microwave therapy is especially helpful for patients who have sprains, strains, herniated discs, rotator cuff tears or arthritis.  Shortwave therapy is often used to treat low back pain, tenosynovitis (inflammation of a tendon sheath) and osteoarthritis of the knee.

Some forms of electrical therapy also provide a thermal effect.

Many people use forms of thermotherapy at home to treat minor conditions, such as a hot pack applied to a stiff neck.

Thermotherapy can be used to treat a number of pain conditions.  These include:

  • (Chronic) muscle spasm.  Persistent and often painful tension and shortness in a muscle or group of muscles that cannot be released voluntarily.
  • ArthritisInflammation of a joint.  Types of arthritis that may benefit from thermotherapy include:

  • Sources of back pain, such as a herniated disc.  A frequently painful condition in which the cartilage (the tough, elastic, fibrous connective tissue) of an intervertebral disc (discs that serve as cushions between the vertebrae) bulges through its protective covering and presses on a nerve.  Most of the time a herniated disc is associated with overlying muscle spasm, which heat therapy decreases.
  • Whiplash and other musculoskeletal types of neck pain.
  • Shoulder pain, such as rotator cuff injuries.  Decreased range-of-motion.  The rotator cuff is made up of the muscles and tendons that connect the humerus to the shoulder blade.  Tendons in the rotator cuff are normally strong, but they can become inflamed and tear as a result of overuse, wear and tear associated with aging or an accident such as a collision.  Another condition that may be eased by application of heat is a frozen shoulder.
  • Other types of joint pain, including many forms of:

    • Arm pain (e.g., tennis elbow)
    • Leg pain (e.g., restless leg syndrome)
    • Knee pain (e.g., injured anterior cruciate ligament)
    • Foot pain (e.g., plantar fasciitis)
  • Tendonitis.  Inflammation of a tendon, a fibrous tissue connecting a muscle with its bony attachment.
  • Bursitis.  Inflammation of a bursa, a sac located between a tendon and a bone.
  • Sprain.  A painful wrenching or laceration of the ligaments of a joint.
  • Eye pain.  An ophthalmologist or other clinician may suggest applying warm compresses to relieve minor conditions such as blepharitis (inflammation of the eyelids).
  • TMJ disorder.  Applications of heat may help tender areas.
  • Chest pain.  Heat can supply relief from disorders such as costochondritis.
  • Abdominal pain and pelvic pain.  Researchers have found that externally applied heat such as hot-water bottles can relieve even deep internal pain for up to an hour by blocking pain receptors.
  • Fibromyalgia.  Therapeutic use of heat may help treat this chronic pain condition, characterized by musculoskeletal aches, Lupus is a chronic autoimmune disease that can cause joint pain and inflammation (arthritis), stiffness, tenderness in soft tissues, general fatigue and sleep disturbances.
  • Other chronic pain disorders, including lupus and myofascial pain syndrome.
  • Asthma
  • Subacute and chronic pain
  • Reduction of joint contractures.

Other conditions that may be treated with heat include back strain or sprain, degenerative disc disease, sciatica and scoliosis, as these conditions are usually associated with muscle spasm.

Heat can also be used as a minimally invasive alternative to surgery.  For example, several treatments for benign prostatic hyperplasia use microwaves, lasers or other sources of heat to destroy excess prostate tissue.  High-intensity heat is also used to destroy some types of benign and cancerous tumors.

In addition, thermotherapy is used to reduce spasticity in neurological conditions.  Recent studies indicate that a combination of thermotherapy and cryotherapy may help stroke patients recover arm function and may ease symptoms in people with heart failure.  Other recent research suggests that a microwave form of thermotherapy might benefit women with advanced cervical cancer.

Counter-Indicators and Warnings

Hot applications such as hot immersion baths, full body heating treatments and hot saunas should be taken with precaution by patients with diabetes, multiple sclerosis, women who are pregnant (this exposes the fetus to prolonged heat) or anyone with abnormally high or low blood pressure.

Contraindications for thermotherapy also apply for acute injuries, circulatory problems in general, poor thermal circulation and areas of the body that are anesthetic.

Thermotherapy generally should not be used during the first several days after an injury, because heat increases blood flow and may worsen swelling.  Heat treatments are inappropriate for some individuals and conditions.  For example, people who have impaired sensation (e.g. from neuropathy due to diabetes) are at risk of burns from overuse of thermotherapy.

Heat therapy should not be used on tissue that has received radiation treatment or on tissue that is directly over a cancer site.

On This Page

Hot Applications:

Hot Applications (Thermotherapy) can help with the following:


Vulvodynia / Vestibulitis

Soothing relief may be obtained by applying warm soaked tea bags to the area.  This can be done by placing the tea bags on menstrual pads to hold them in place or you can take a sitz bath in which tea bags have been soaked.


Boils, Abscesses, Carbuncles

The main treatment for most boils is heat application, usually with hot soaks or hot packs.  Heat application increases the circulation to the area and allows the body to better fight off the infection.  Apply warm, moist compresses for 20 minutes, 4 times a day to encourage circulation and resolution.  Take showers instead of baths (baths can spread infection) and keep the boil covered with a clean bandage.

As long as the boil is small and firm, opening the area and draining the boil is not helpful, even if the area is painful.  However, once the boil becomes soft or "forms a head" (that is, a small pustule is noted in the boil), it is ready to drain.  Once drained, pain relief can be dramatic.  Most small abscesses, such as those that form around hairs, drain on their own with soaking.  On occasion, and especially with larger boils, these will need to be drained or "lanced" by a healthcare practitioner.  Frequently, these larger boils contain several pockets of pus that must be opened and drained.

Cold Or Flu

One way of enhancing the immune system is by using different forms of heat.  A common way of avoiding colds is to take a good hot soak periodically during cold weather followed by a quick cooling rinse.  Another method is to take a sauna followed by a cold shower.  This hot-cold cycle is usually repeated at least twice and works best if done at the very first indication of a viral infection.


Osgood-Schlatter Disease

If your pain is mild, you can probably continue to participate in your sport.  Using a heating pad or warm, moist compresses at the site for 15 minutes before activity and/or using ice for 20 minutes after activity may help.


Ice packs or heating pads – whichever technique helps to decrease the pain – may help you to better manage the pain of costochondritis.

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