Introduction[edit | edit source]
Infrared (IR) or thermal radiation is a band of energy in the complete electromagnetic spectrum. IR are the radiations of longer wavelength than the red end of the visible spectrum and extend to the microwave region, i.e., from 760 nm to 1 mm. IR radiation is generated by Sun. Many ancient therapies have utilized sunlight for wound healing and pain relief. When Sun rays reach the ground, they get absorbed by gases or water molecules in the atmosphere. The human body is made of 70% water, so it can potentially accumulate a large amount of energy that could modulate biological processes by strong resonant absorption of IR radiation from sunlight mediated by water molecules.
Any heated body emits infra red. Any material with temperature above absolute zero emits IR. IR radiations are produced in all matter by molecular vibration; the molecular movement causes infrared emission of different wavelengths and frequencies. The frequencies at which maximum radiations are emitted are proportional to the temperature which means the higher the temperature, the higher the frequency and so shorter the wavelength. 
IR includes wavelengths between the 780 nm to 1000 μm. IR is divided into different bands: Near-Infrared (NIR, 0.78~3.0 μm), Mid-Infrared (MIR, 3.0~50.0 μm) and Far-Infrared (FIR, 50.0~1000.0 μm) as defined in standard ISO 20473:2007 Optics and photonics -- Spectral bands.Classification
The classification of the International Commission on Illumination (CIE) has three sub-divisions for the IR radiation
|Type||Wavelength||Photon energy (THz)|
|IR A (Near IR)||0.7– 1.4 μm (700-1400nm)||215– 430|
|IR B (Mid-IR)||1.4– 3.0 μm (1400-3000nm)||100– 215|
|IR C (Far-IR)||3.0– 100 μm (3000 nm– 0.1 mm)||3– 100|
An alternative classification provided in ISO 20473 
The Near infrared are also known as 'luminous' as they have some visible light with wavelength of 770 to 1500 nanometers. The luminous source is found to be more effective in tissue-heating as it penetrates deeper and energy is distributed in larger areas of the tissues.
The Far infrared (FIR) also called non-luminous are within 1500nm to 0.1 mm. The non-luminous with peak around 4000nm is absorbed in the skin. FIR wavelength is too long to be perceived by the eyes, however, the body experiences its energy as a gentle radiant heat which can penetrate up to 1.5 inches (almost 4 cm) beneath the skin. A randomised controlled trial found FIR effective in reducing chronic low back pain. Another clinical prospective randomized comparative study showed FIR after arthroscopic rotator cuff repairs effectively and safely reduced postoperative pain, thereby facilitating rehabilitation and better ROM in the early postoperative period. A systematic review suggests that FIR therapy may be a beneficial complementary treatment for some chronic diseases, including cardiovascular disease, diabetes mellitus, and chronic kidney disease.
Production of Infrared[edit | edit source]
Different kinds of lamps are used for production of therapeutic infrared:
Non-luminous generator - An electric current is passed through a coil of wire wound on an insulating material (like porcelain/fireclay) which produces heat. The infrared emitter is placed at the focus of parabolic reflector to reflect the radiations in an uniform beam. The heated wire and heated material emits IR. Non-luminous requires some time to heat up before the emitted rays reach maximum intensity and so must be switched on at an appropriate time prior to use .
Luminous generators - IR is produced by incandescent lamps in the luminous generator. The lamp consists of a wire filament (tungsten) enclosed in a glass bulb that may be evacuated or filled with an inert gas at a low pressure. When an electric current is passed through the tungsten filament, it gets heated and emits IR, visible and few ultra-violet (UV) rays. The front of the bulb is red to filter out shorter visible and UV rays.
Power varies, for smaller lamps is 250 to 500 W for both generators and for large non luminous - 750 or 1000W and large luminous 600 to 1500 W.
Absorption and Penetration of IR[edit | edit source]
Some rays are reflected from the skin surface. Some penetrate in the skin, get scattered, refracted and ultimately absorbed in tissues. Water and protein in the tissues strongly absorb IR. Research suggests penetration of IR depends on the structure, vascularity, pigmentation of skin and wavelength of the rays. Penetration depth is the depth at which approximately 63% of radiation energy is absorbed. Far infrared rays penetrate up to 1.5 inches (almost 4 cm) beneath the skin.
Physiological Effects[edit | edit source]
Infrared radiations cause:
- local cutaneous vasodilation due to the release of chemical vasodilator (histamine) as well as possible effect on the blood vessels, occurs after 1-2 mins
- evident erythema. The rate and intensity of erythema depends on rate and degree of heating.
- reflex dilation of other cutaneous vessels occurs to maintain normal heat balance
- prolonged heating leads to sweating and eventually to cooling
Therapeutic Uses[edit | edit source]
Infrared is used for the following purposes:
- pain relief
- decreases muscle spasm
- increases the sensory nerve conduction velocity, increase in endorphins influencing the pain gate mechanism
- acceleration of healing and tissue repair- pressure sores
- used prior to electrical stimulation/testing or biofeedback to make the skin a better conductor
Application[edit | edit source]
Patient is placed in a comfortable position and the area to be treated is exposed. Nature and effects of treatment are explained. Skin is examined and thermal sensations are tested. Eyes are shielded in case they are irradiated. To achieve maximum penetration, the lamp is placed at right angles to area to be treated.Distance from the lamp can be about 60-75 cm for large lamp (750-1000W) and 45-50cm for smaller ones. Intensity of heat is controlled by altering the position of the lamp or in some lamps by altering the resistance thereby the current to the element. Non-luminous lamp has to be switched on up to 15 mins before application to allow maximum emission.
Infrared Emitting Materials for Clothing[edit | edit source]
Sports professionals, especially elite athletes, use far-infrared (FIR)-emitting garments to enhance exercise performance and recovery. Garments absorb body-emitted heat energy, and then re-emit it through radiation (within the FIR wavelength range) back to the body.  Literature suggests use of bio-ceramic materials, also called as Far-Infrared Emitting Ceramic Materials for post-exercise recovery. Bioceramics are produced by the combination of oxides which emit FIR. Far infrared emitting polymers or ceramic nanoparticles are incorporated into sports apparels which help in reducing pain and inducing tissue repair. 30-minutes whole-body exposure to far-infrared after performing running protocol to induce muscle damage showed FIR reduced pain (post 48 hours) and caused knee extension maximal voluntary contraction capacity recovery (post 24 hours) in highly trained runners.  However there are conflicting evidence regarding recovery. A recent systematic review shows studies investigating similar outcomes related to exercise performance or recovery were scarce and results inconclusive, which prevents from drawing firm conclusion about the utilisation of FIR-emitting garments in athletes.
Far infrared Saunas[edit | edit source]
In FIR Sauna, the heating elements are typically heated to about 300– 400° C. The heat exchange between the body and the environment is almost purely radiative (radiant heating), with the cabin air temperature at around 40°C or less. This is also called as “Waon therapy” and frequently in Japan. Waon therapy means the body is warned in an IR chamber for 15 min at 60°C, and then they are wrapped in thermal blankets and laid down to maintain heat for an additional 40 min, and finally patient drinks water to replenish moisture lost by perspiration. It can improve cardiac function and is useful in rehabilitation.
Far-infrared saunas could be applied as an alternative to moderate exercise in sedentary patients suffering from osteoarthritis or cardiovascular, respiratory problems. Literature shows extensive use of Waon therapy in various conditions for cardiovascular conditions and diseases, particularly chronic heart failure, chronic obstructive pulmonary disease, type II diabetes and peripheral arterial disease 
Dangers[edit | edit source]
Contraindications[edit | edit source]
- Impaired cutaneous thermal sensations
- Defective arterial cutaneous circulation
- Dermatitis or eczema
- Skin damage due to ionizing radiation
Summary[edit | edit source]
Infrared promotes a wide range of therapeutic benefits in cells or tissues. It helps to reduce pain and can be used to treat various conditions. Research suggests it is a safe, effective to manage pain without medication.
References[edit | edit source]
- Infrared and visible radiations. Electrotherapy Explained principles and practice. John Low & Ann Reed. 2nd edition.
- Tsai SR, Hamblin MR. Biological effects and medical applications of infrared radiation. Journal of Photochemistry and Photobiology B: Biology. 2017 May 1;170:197-207.
- Vatansever F, Hamblin MR. Far infrared radiation (FIR): its biological effects and medical applications. Photonics & lasers in medicine. 2012 Nov 1;1(4):255-66.
- Thermal agents in rehabilitation. Chapter 5 Biophysical Principles of heating.
- Gale GD, Rothbart PJ, Li Y. Infrared therapy for chronic low back pain: a randomized, controlled trial. Pain Research and Management. 2006 Jan 1;11(3):193-6.
- Yoon JY, Park JH, Lee KJ, Kim HS, Rhee SM, Oh JH. The effect of postoperatively applied far-infrared radiation on pain and tendon-to-bone healing after arthroscopic rotator cuff repair: a clinical prospective randomized comparative study. The Korean Journal of Pain. 2020 Oct 1;33(4):344.
- Shui S, Wang X, Chiang JY, Zheng L. RETRACTED: Far-infrared therapy for cardiovascular, autoimmune, and other chronic health problems: A systematic review. Experimental Biology and Medicine. 2015 Oct;240(10):1257-65.
- Methods of Heating the Tissues. Clayton's Electrotherapy
- Bontemps B, Gruet M, Vercruyssen F, Louis J. Utilisation of far infrared-emitting garments for optimising performance and recovery in sport: Real potential or new fad? A systematic review. PloS one. 2021 May 6;16(5):e0251282.
- Nunes RF, Dittrich N, Duffield R, Serpa MC, Coelho TM, Martins DF, Guglielmo LG. Effects of Far‐Infrared Emitting Ceramic Material Clothing on Recovery after Maximal Eccentric Exercise. Journal of human kinetics. 2019 Nov;70:135.
- Hausswirth C, Louis J, Bieuzen F, Pournot H, Fournier J, Filliard JR, Brisswalter J. Effects of whole-body cryotherapy vs. far-infrared vs. passive modalities on recovery from exercise-induced muscle damage in highly-trained runners. PloS one. 2011 Dec 7;6(12):e27749.