The Healing Power of Heat

Local heat can be applied in various forms, including fomentations, paraffin baths for the hands or feet, hot footbaths, hot compresses, and hot water bottles. Heat therapy is typically soothing and can provide psychological relaxation. It promotes local healing and alleviates painful muscle spasms. In this blog, we explore the scientific reasons for using localized heat applications for healing, particularly in relation to hydrotherapy.healing especially as it relates to hydrotherapy.

Heat Aids Circulation

Moist heat increases tissue metabolism. Because of this increase in tissue metabolism, there is an increase in carbon dioxide and hydrogen ion concentration, but a decrease in oxygen concentration. This change prompts the blood vessels to open up so that more oxygen can come into the tissue through the blood and then through the interstitial fluid (the fluid between cells). Heat increases oxygen uptake and accelerates tissue healing. It improves blood flow to the skin and blood vessels. Heat, therefore, enhances the delivery of oxygen and nutrients to the tissues.
Note: Moist heat applications increase blood flow to an area four to five times more than dry heat applications.¹

Prolonged heat applications to the reflex area of the skin usually produce passive dilation of blood vessels in the corresponding organ. For example, a prolonged hot application to the pelvis relaxes the muscles of the bladder, rectum, and uterus and dilates the blood vessels. In women, it increases menstrual blood flow.

Heat Speeds Up Enzymes

In most cases, moist heat revs up enzymes (proteins that speed up a chemical reaction). They are essential to life. Here is an example of how heat from a hydrotherapy treatment can influence enzymes: Lysozyme is an enzyme that degrades bacterial cell walls. It also exerts some cancer-fighting activity.² Lysozyme and other germ-fighting molecules (such as hydrogen peroxide) are found in the lysosomes of phagocytes (special white blood cells that capture and eat bacteria). Once a phagocyte captures and ingests germs, a cavity (phagosome) forms and surrounds the germ. The phagosome holds bacteria or debris. Then lysosomes approach. The lysosomal enzymes, including lysozyme, destroy the contents of the phagosome.

Something to Consider

Please note that hot applications of any kind lower the alkalinity of the blood or tissue in the area to which heat is applied. This helps lysozymes to work and phagocytes to become more efficient. Hydrogen peroxide is another enzyme found in the lysosomes of phagocytes.³ We should note that this shift in the alkalinity of the blood does not do any damage because the normal pH level of the blood (7.35 to 7.45) is still maintained and any changes are temporary.

Metabolism

Metabolism is the sum of all the chemical and physical processes going on inside the body. Moist applications of heat to a local area increase local metabolism. Heat can even increase the body’s temperature if the hydrotherapy tool used is very hot and a large area is treated.

Effects of Heat on the Skin

Heat increases moisture in the skin and improves blood flow to the skin. It increases the production of nitric oxide in the skin blood vessels. Nitric oxide is a molecule that promotes vasodilation.. The maximum temperature of the skin is obtained after eight minutes.⁴

Something to Consider

Please note that since most fomentations only hold heat for 3 to 5 minutes, the hydrotherapist would need to apply a second fomentation, or in the case of a revulsive treatment apply it before the fomentation starts to cool off. A gradually cooling fomentation is a sedative. For a contrast hot and cold treatment, you want a sharp contrast between a hot fomentation and ice-cold water.

Connective Tissue

Heat makes the connective tissue in tendons and ligaments more elastic.⁵

Consensual Reflex (Contralateral Reflex Effect)

Heat to one extremity also causes vasodilation in the other.⁶ So, if your right arm is broken and in a cast, by doing hot and cold on your left arm you can improve the circulation and hasten healing in your casted right arm.

Heat to the Abdomen

Heat to the abdomen reduces the production of stomach acid, decreases intestinal blood flow, and decreases intestinal movement.⁷ Never apply heat to the abdomen if acute abdominal pain is present.

Heat Improves Urinary Output

A hot application to either the lower, anterior abdomen or prolonged heat over the kidneys increases urine output (diuresis). ⁸ This could benefit a person with high blood pressure. Anything that decreases the blood flow to the kidneys increases blood pressure.

Heat and the Lungs

Heat on the chest makes breathing easier and aids in expectoration. ⁹ Do not apply heat to the chest of somebody who has pulmonary edema, active tuberculosis, or is coughing up blood. Do not apply heat to the chest of a patient who has congestive heart failure, without a doctor’s order.

Prolonged Heat over the Heart

Heat over the precordium (area over the heart and lower chest) increases the heart rate and reduces the force of contraction.¹⁰ if a person has congestive heart failure and pneumonia, an ice bag can be placed over the heart beneath the fomentation to slow down the heart rate if the person doesn’t have coronary artery disease. As cold constricts arteries, it is unwise to apply a cold ice pack over the heart area.

I remember one patient who had a heart rate of 44 after surgery. I put a hot fomentation on her chest, which increased her heart rate to 60.

Heat and the Skeletal Muscular System

Heating treatments improve the helpful creation of new blood vessels in skeletal muscles (angiogenesis), promote muscle hypertrophy, increase the number of mitochondria in the cells, and improve glucose metabolism in the skeletal muscles. Both local and whole-body heat therapy increases mitochondrial efficiency, improves insulin sensitivity, and decreases muscle wasting caused by inactivity.¹¹Heat relieves muscle spasms and exercise-induced muscle fatigue. Additionally, heat therapy improves blood flow, glycogen and protein synthesis, and the removal of waste byproducts from skeletal muscles.¹²

Heat Improves the Efficiency of the White Blood Cells

The application of heat improves the mobility of the white blood cells to the targeted area. As the body temperature rises, the chemical attraction of the phagocytes toward the infection improves. The phagocytosis of bacteria is increased as is the enzymatic destruction of the germs by the lysosomal enzymes.

Not All Heat is Created Equal

The efficiency of a hot application varies due to several factors. The effects of heat application depend on the following factors.((Sinclair, ibid)
• The skin temperature at the beginning of a treatment.
• How hot the application is: the hotter the application is, the faster the reaction will be.
• The padding of towels between the hot application and the body.
• The duration of the hot application: the shorter the hot application is applied, the more stimulating is the effect.
• The part of the body being treated: the skin on the feet has more hot and cold receptors than the skin on the chest.
• How wide an area is covered by the application of moist heat has an effect: the larger the application of moist heat, the faster the reaction is.
• Use of friction will increase the body’s response to heat.
• Not everybody responds in the same way and to the same extent. So be observant!

Menopause

During menopause, changes in reproductive hormone levels substantially alter how the skin regulates temperature via control of the skin’s blood flow. This altered control might contribute to the occurrence of hot flashes. Women going through menopause might not tolerate heat as well as younger women.

Hyperthyroidism

Individuals with hyperthyroidism do not tolerate heat well.

Diabetes and Peripheral Vascular Disease

Individuals with diabetes often develop peripheral vascular disease, atherosclerosis, or arteriosclerosis in the arteries of their extremities.¹³ Like a hot foot bath as an example; heat increases metabolism in the feet and lower legs. The increased metabolism increases oxygen consumption and consequently reduces the oxygen concentration and increases the by-products of metabolism (carbon dioxide and hydrogen). Normally, a decrease in oxygen concentration accompanied by an increase in the concentration of carbon dioxide and hydrogen ions will cause blood vessels in the feet and lower legs to dilate so that fresh blood cruises into the feet. However, if a person has atherosclerosis in their lower extremities their blood vessels cannot dilate optimally. When one increases oxygen demand without increasing oxygen supply, pain can result. Always use a thermometer to test the temperature of the water. Do not go above 100-102◦F while giving a person with peripheral vascular disease or diabetes any type of bath.

Obesity

Because obese individuals have more adipose tissue above their muscles, it may take longer for local heat to penetrate their tissues and heat to dissipate. Obese individuals may respond to whole body heat much faster than those who have a regular weight.

Neuropathy

An individual with this disease cannot sense hot or cold accurately and is in danger of being burned by a fomentation. Hot and cold applications are usually contraindicated on areas where the neuropathy is present. Foot baths of 102◦F or less, neutral tub baths, and salt glow treatments may be used for individuals who have neuropathy.

Contraindications for the Use of Heat

• Do not perform any hydrotherapy unless you have a diagnosis. If you place a hot water bottle or a fomentation on the abdomen of a person who has appendicitis, you can cause his appendix to rupture. Do not apply heat over an enlarged spleen.
• Use only mild heat applications caution to areas of the skin where pain cannot be felt, or with patients who cannot perceive or communicate how they are feeling or are reacting to the treatment. It is safer to use water rather than a fomentation on areas affected by neuropathy.
• Do not apply heat over areas that are bleeding. Heat over the lower abdomen during painful menstrual cramps may be the exception. Do you apply heat to the abdomen if there is blood in the stool or an bleeding peptic ulcer
• Do not use heat in conditions of acute inflammation where swelling is pronounced or edema is present. Edema is a condition characterized by an excess of watery fluid collecting in the cavities or tissues of the body.
• Heat increases capillary permeability and increases swelling. The formation of edema is facilitated by heat and is decreased by cooling.
• Ischemic tissue (that with inadequate blood supply typical seen in peripheral vascular disease and severe diabetes) should not be overheated. In those cases, use warm, not hot compresses.
• No one who has diabetes should have heat applied on their extremities if they have neuropathy or peripheral vascular disease unless under the direct prescription and oversight of his physician. While many diabetic individuals could tolerate a hot footbath of 102 ◦F or less, some would not, especially if the pulse in the feet is diminished. Fomentations are usually not to be used on any area where neuropathy or swelling is present.
• Since heat produces an increase in blood flow, heat should not be used with a person who tends to bleed, not near any local tissue that is bleeding, nor on a person who is receiving an anticoagulant.
• Heat should not be applied on the abdomen of a pregnant woman. It could overheat her ovaries or the developing fetus. This is particularly important in early pregnancy. In pregnancy, elevation of the entire body temperature, as in hyperthermia treatments, should also be avoided.
• Do not apply heat over an enlarged thyroid gland, enlarged spleen, or bulging intervertebral discs.

Note: Heat is also not suitable for acute conditions requiring emergency medical care, such as heart attacks, strokes, appendicitis, or bowel obstructions, or pending pulmonary edema. Diagnosis, the patient’s medical history, current condition, physical exam with pertinent lab and radiological studies are needed to determine which hydrotherapy treatment is best for the patient.

 

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3. Thrash, Agatha. Home Remedies, 2005,p.44[↩]
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5. Sinclair, Modern Hydrotherapy for Massage Therapist, p.56-57.[↩]
6. Sinclair, Modern Hydrotherapy for Massage Therapist, p.56-57.[↩]
7. Sinclair, Modern Hydrotherapy for Massage Therapist, p.56-57.[↩]
8. Moor, Fred B. Manual of Hydrotherapy and Massage, 1964.[↩]
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12. Kim K, Monroe JC, Gavin TP, Roseguini BT. Skeletal muscle adaptations to heat therapy. J Appl Physiol (1985). 2020 Jun 1; 128(6):1635-1642. doi: 10.1152/japplphysiol.00061.2020.[↩]
13. Baldwin, B., The Physiology of Heat, Wildwood CHE class, 2009.[↩]