Infrared (IR) or thermal radiation is a band of energy across the electromagnetic spectrum. IR is radiation with longer wavelengths than the red end of the visible spectrum and extends into the microwave region, i.e. from 760 nm to 1 mm.  Infrared radiation is produced by the sun. many ancient Therapy uses sunlight to heal wounds and relieve pain. When the sun’s rays reach the ground, they are absorbed by gases or water molecules in the atmosphere. The human body is made up of 70% water, so it may accumulate a lot of energy to regulate biological processes Strong resonant absorption of solar infrared radiation mediated by water molecules .
Any heated object emits infrared light. Any material with a temperature above absolute zero emits infrared light. Infrared radiation is generated in all substances by molecular vibrations; molecular motions cause infrared emissions of different wavelengths and frequencies . Frequency of maximum radiation The emitted light is proportional to temperature, which means that the higher the temperature, the higher the frequency and the shorter the wavelength. 
IR includes wavelengths between 780 nm and 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 standard ISO 20473:2007 Optics and Photonics – – Spectral Bands .  classification
The International Commission on Illumination (CIE) classification has three subclasses for infrared radiation 
Type Wavelength Photon Energy (THz)IR A (Near IR)0.7– 1.4 μm (700-1400nm)215– 430IR B (Mid-IR)1.4– 3.0 μm (1400-3000nm)100– 215IR C (Far-IR)3.0 – 100 μm (3000 nm– 0.1 mm)3– 100
Alternative classification provided in ISO 20473 
Type Wavelength (μm)Near IR0.78-3MidIR3-50Far IR50-1000
Near-infrared rays are also called “luminescence” because they have some visible light with wavelengths between 770 and 1500 nanometers.  found that a luminescent source is more effective at tissue heating because it penetrates deeper and distributes energy over a larger area of tissue .
Far infrared (FIR) is also called non-luminous, between 1500nm and 0.1mm. Non-luminescent substances with a peak around 4000nm are absorbed by the skin . FIR wavelengths are too long to be perceived by the eye, but the body perceives its energy as mild radiant heat that can penetrate up to 1.5 inches (nearly 4 cm) under the skin . A randomized controlled trial found FIR to be effective in reducing chronic low back pain.  Another clinical prospective randomized comparative study showed that FIR after arthroscopic rotator cuff repair effectively and safely reduced postoperative pain, thereby Promotes recovery and better ROM in the early postoperative period.  A systematic review showed that FIR therapy may be a beneficial complementary therapy for several chronic diseases, including cardiovascular disease, diabetes, and chronic kidney disease. 
Production of Infrared
Different kinds of lamps are used to produce therapeutic infrared rays:
Non-luminous Generator – Electricity is passed through a coil wound around an insulating material such as porcelain/fireclay, generating heat. An infrared emitter is placed at the focal point of the parabolic reflector to reflect the radiation into a uniform beam. Heating wire and heating The material emits infrared light. Non-glow takes some time to heat up before the emitted light reaches its maximum intensity, so it must be turned on at an appropriate time before use  .
Luminescence Generator – Infrared light is produced by an incandescent lamp in a luminescence generator. The lamp consists of a filament (tungsten filament) enclosed in a glass bulb that can be evacuated or filled with an inert gas at low pressure. When current is passed through the tungsten wire, it gets Heats up and emits infrared visible light and a small amount of ultraviolet (UV) light. The front end of the bulb is red to filter out the shorter visible and ultraviolet rays .
For smaller lamps, the power generator is 250 to 500 W, for large non-luminous lamps – 750 or 1000W, and for large glowing lamps – 600 to 1500 W.
Absorption and Penetration of IR
Some rays reflect off the surface of the skin. Some substances that penetrate into the skin scatter the refraction and are eventually absorbed by the tissue. Water and proteins in tissues strongly absorb infrared rays. Studies have shown that the penetration of infrared light depends on the skin’s structural vascular pigmentation and wavelength Rays. Penetration depth is the depth at which approximately 63% of the radiant energy is absorbed.  Far infrared rays can penetrate up to 1.5 inches (nearly 4 cm) below the skin .
Factors of Infrared Absorption and Transmission
- Wavelength of rays
- Angle of incidence of ray
- Distance from source of infrared
- Density of tissue 
Infrared radiations cause:
- Local skin vasodilation occurs after 1-2 minutes due to release of chemical vasodilators (histamine) and possible effects on blood vessels.
- Prominent erythema. The speed and intensity of erythema depend on the rate and degree of heating.
- Reflex dilation of other skin blood vessels occurs to maintain normal thermal balance.
- Prolonged heating can lead to sweating and eventually cooling.
Infrared light is used for the following purposes :
- pain relief
- decreases muscle spasm
- Increased sensory nerve conduction velocity increases endorphins affect pain gate mechanism
- Accelerated Healing and Tissue Repair – Pressure Ulcers
- Use before electrical stimulation/testing or biofeedback to make skin a better conductor
Position the patient in a comfortable position and expose the area to be treated. The nature and effects of the treatment are explained. Examine the skin and test for thermal sensation. Eyes are shielded from radiation. For maximum penetration, lights are placed at right angles  The distance between the headlight (750-1000W) and the light is about 60-75cm, and the distance between the small light is about 45-50cm. The heat intensity is controlled by changing the position of the lamp or, in some lamps, by changing the resistance and thus the current flow to the element. Non-luminous lamps must Leave on up to 15 minutes before application to allow for maximum discharge.
Infrared Emitting Materials for Clothing
Sports professionals, especially elite athletes, use far infrared (FIR) emitting apparel to enhance athletic performance and recovery. Clothing absorbs thermal energy emitted by the body and reradiates it back to the body through radiation (in the FIR wavelength range).  The literature recommends using Bioceramic materials used for post-exercise recovery are also known as far-infrared emitting ceramic materials . Bioceramics are made by combining oxides that emit far infrared rays. Far-infrared emitting polymers or ceramic nanoparticles are incorporated into sportswear to help reduce Pain and induced tissue repair . Whole-body exposure to far-infrared radiation for 30 minutes following a running regimen to induce muscle damage showed that far-infrared radiation reduced pain (after 48 hours) and resulted in recovery of maximal voluntary contraction capacity for knee extension in trained runners (after 24 hours) .  However, there is conflicting evidence regarding recovery. A recent systematic review showed that studies investigating similar outcomes related to athletic performance or recovery were few and inconclusive, preventing definitive conclusions regarding the utilization of far-infrared emissions Athlete’s clothing. 
Far infrared Saunas
In a FIR sauna the heating elements are usually heated to around 300–400°C. The heat exchange between the body and the environment is almost purely radiative (radiant heating), with indoor air temperatures of around 40°C or lower. This is also known as “Waon Therapy” and I often go to Japan. Waon therapy means that the body is warned in an infrared chamber at 60°C for 15 minutes, they are then wrapped in a thermal blanket and lie down to retain the heat for another 40 minutes, and finally the patient drinks water to replace fluid lost through sweating . it can improve Cardiac function, contribute to rehabilitation .
For sedentary patients with osteoarthritis or cardiovascular respiratory disease, far-infrared saunas can be an alternative to moderate exercise.  The literature shows that Waon therapy is widely used in various conditions of cardiovascular disease and disease, especially Chronic Heart Failure Chronic Obstructive Pulmonary Disease Type II Diabetes Mellitus and Peripheral Arterial Disease 
- Skin irritation
- Eye damage
- Low BP
- Electric shock
- Defective arterial blood flow
- Rheumatoid arthritis
- Ankylosing spondylitis
- Joint stiffness
- Muscle spasm 
- Impaired cutaneous thermal sensations
- Defective arterial cutaneous circulation
- Dermatitis or eczema
- Skin damage due to ionizing radiation
- Mental retardation
- Metal implant
Infrared light promotes a wide range of therapeutic benefits in cells or tissues. It helps relieve pain and is used in the treatment of various ailments. Research shows that treating pain without medication is safe and effective.
- ↑ Jump up to:1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Infrared and visible radiations. Electrotherapy Explained principles and practice. John Low & Ann Reed. 2nd edition.
- ↑ Jump up to:2.0 2.1 2.2 2.3 2.4 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.
- ↑ Jump up to:3.0 3.1 3.2 3.3 3.4 3.5 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.
- ↑ Jump up to:8.0 8.1 Methods of Heating the Tissues. Clayton’s Electrotherapy
- ↑ Jump up to:9.0 9.1 Val Robertson, Alex Ward, John Low John Low Ann Reed, Electrotherapy Explained: Principles and Practice. 4th Edition. Butterworth-Heinemann,2006
- ↑ Jump up to:10.0 10.1 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.