Infrared light is a type of electromagnetic radiation with wavelengths longer than visible red light, ranging from about 700 nanometers to 1 millimeter. You can’t see it with your eyes, but you feel it every day as warmth. The heat you sense radiating from a campfire, a sunlit sidewalk, or another person’s body is largely infrared radiation. It sits just beyond the red end of the visible spectrum, which is where it gets its name (“infra” meaning “below” in Latin, as in below the frequency of red).
Where Infrared Fits on the Spectrum
Light travels in waves, and the electromagnetic spectrum organizes all types of light by wavelength. Radio waves have the longest wavelengths, gamma rays the shortest. Infrared occupies the band between visible light and microwaves, spanning wavelengths from about 0.7 micrometers (700 nanometers) up to 1,000 micrometers (1 millimeter), according to NASA’s classification.
Infrared is classified as non-ionizing radiation. That means its photons don’t carry enough energy to knock electrons off atoms or break chemical bonds in DNA the way X-rays or ultraviolet light can. Visible light and infrared only cause tissue damage through high-intensity, multi-photon interactions, not through the single-photon DNA disruption that makes UV and ionizing radiation a cancer risk.
The Three Subtypes of Infrared
Scientists break the infrared band into three broad regions, though the exact boundaries vary depending on the field and the detector technology being used.
- Near-infrared (about 0.7 to 5 micrometers): The closest to visible light and the type used in TV remotes, fiber optic communication, and many therapeutic devices. It penetrates tissue more deeply than longer infrared wavelengths.
- Mid-infrared (about 5 to 25 micrometers): Useful in chemical analysis and gas detection because many molecules absorb strongly at these wavelengths. Night-vision and heat-seeking technologies often operate in this range.
- Far-infrared (about 25 to 350 micrometers): Associated with the gentle warmth emitted by the human body and warm objects. This is the type used in infrared saunas and some therapeutic heating devices.
How Infrared Transfers Heat
Infrared heating works differently from a conventional oven or a hot water bottle. Instead of warming the surrounding air first and waiting for that air to heat an object, infrared radiation travels as an electromagnetic wave directly to whatever it strikes. The energy converts to heat only when it’s absorbed by a material. This is why standing in front of a heat lamp feels warm on your skin while the air around you stays relatively cool.
This direct transfer has practical advantages. It’s faster and more energy-efficient than heating methods that rely on warming the air first. Industrial food processing, paint curing, and even patio heaters all exploit this principle. Your body uses the same mechanism constantly: roughly half the energy you radiate away is emitted as infrared light.
What Infrared Does Inside the Body
When near-infrared or red light penetrates skin, it reaches structures inside cells called mitochondria, the components responsible for producing energy. A specific protein in the mitochondrial chain absorbs these photons, which enhances cellular respiration and increases production of ATP, the molecule cells use as fuel. Hours after exposure, secondary effects follow: nitric oxide separates from its binding site (which helps relax blood vessels), and the overall energy pool within the cell shifts upward.
Far-infrared exposure has been studied for its effects on blood flow and inflammation. Several weeks of far-infrared sauna therapy significantly improved the ability of arteries to dilate in response to increased blood flow, a key marker of vascular health. In patients with coronary risk factors, two weeks of far-infrared dry sauna use measurably reduced a biomarker of oxidative stress (a byproduct of the kind of cellular damage linked to chronic disease). Similar reductions were observed in patients with type 2 diabetes who received local far-infrared therapy on their legs. Animal studies have shown that far-infrared exposure increases capillary density, boosts blood flow, and triggers the production of protective anti-inflammatory proteins in tissues.
Common Uses of Infrared Technology
Infrared light shows up in more everyday technology than most people realize. TV remotes use near-infrared LEDs to send signals. Thermal imaging cameras detect mid- and far-infrared radiation to create heat maps, which is why firefighters can find people through smoke and building inspectors can spot insulation gaps in walls. In medicine, infrared thermography has been used to help diagnose breast cancer, diabetic nerve damage, and peripheral vascular disorders by mapping temperature differences across the body’s surface.
Infrared saunas have become one of the most visible consumer applications. Unlike traditional saunas, which heat the air to between 150°F and 195°F, infrared saunas operate at lower temperatures, typically 120°F to 140°F. They warm your body directly through infrared panels rather than superheating the surrounding air. Many people find this more tolerable while still producing a deep sweat.
Near-infrared and red light therapy devices, now widely available for home use, are marketed for skin health, muscle recovery, and joint pain. These typically use LEDs or low-level lasers to deliver specific wavelengths thought to stimulate the mitochondrial pathways described above.
Safety and Exposure Limits
Because infrared is non-ionizing, it doesn’t carry the DNA-damage risks associated with ultraviolet light or X-rays. The primary hazard from infrared is thermal: too much concentrated infrared energy can burn skin or damage eyes.
Your eyes have a natural protective reflex that limits exposure to bright infrared sources (like looking near the sun) to a fraction of a second. But prolonged occupational exposure is a different story. Workers exposed to high-intensity infrared environments, such as glassblowers and steel workers, historically developed cataracts after daily exposure over 10 to 15 years. The International Commission on Non-Ionizing Radiation Protection recommends that infrared exposure in the near-infrared range (770 nanometers to 3 micrometers) stay below 10 milliwatts per square centimeter for exposures lasting longer than about 17 minutes.
For typical consumer products like infrared saunas, heating panels, and red light therapy devices, the intensity falls well below these industrial thresholds. The main precaution is avoiding direct, prolonged eye exposure to concentrated infrared sources and following manufacturer guidelines on session length. People with heat-sensitive conditions or those taking medications that affect skin sensitivity should be more cautious with any heat-based therapy.
Why Everything Warm Glows in Infrared
Every object with a temperature above absolute zero emits some infrared radiation. The warmer the object, the more infrared it produces and the shorter the peak wavelength becomes. Your body, at around 98.6°F, radiates primarily in the far-infrared range. A hot stove emits shorter-wavelength infrared. Heat something enough, around 900°F or more, and it begins emitting wavelengths short enough to see as a dull red glow. This is the same principle that makes stars visible: they’re so hot their radiation peaks in the visible or even ultraviolet range.
This relationship between temperature and infrared emission is what makes thermal cameras work. They don’t “see” heat exactly. They detect the infrared radiation that warm objects naturally emit and convert it into a visible image. A person walking through a cold room stands out vividly because their body radiates far more infrared energy than the cooler walls and furniture around them.