The Science Behind Infrared Heat Therapy

Infrared saunas have grown enormously in popularity, but marketing claims often outpace scientific understanding. To truly appreciate what an infrared sauna can—and cannot—do, it helps to understand the underlying physics and biology at play.

This guide explores the science of infrared heat therapy: what infrared radiation is, how it interacts with human tissue, and what happens in your body during an infrared sauna session. Understanding these mechanisms helps you evaluate claims critically and use your sauna more effectively.

Understanding the Electromagnetic Spectrum

Infrared radiation is part of the electromagnetic spectrum—the continuum of energy waves that includes everything from radio waves to gamma rays. The spectrum is divided by wavelength, with longer wavelengths carrying less energy per photon and shorter wavelengths carrying more.

Infrared sits between visible light (which we can see) and microwaves. It's further divided into three categories:

• Near-infrared (NIR): 700nm - 1,400nm wavelength
• Mid-infrared (MIR): 1,400nm - 3,000nm wavelength
• Far-infrared (FIR): 3,000nm - 100,000nm wavelength

The "infrared" in infrared saunas primarily refers to far-infrared (FIR), though full-spectrum models also emit near and mid-infrared wavelengths.

How Infrared Penetrates Tissue

Different wavelengths of infrared penetrate tissue to different depths, which explains why each type is associated with different effects:

Near-Infrared Penetration

NIR wavelengths penetrate the deepest into tissue—up to several centimetres—because water absorbs them less effectively. However, much of this energy is scattered rather than absorbed uniformly. NIR interacts primarily with mitochondria, the energy-producing structures within cells, potentially stimulating cellular metabolism.

Mid-Infrared Absorption

MIR wavelengths are absorbed more readily by water molecules in tissue, limiting penetration but providing effective heating of the water-rich layers beneath the skin's surface—including muscles and joints.

Far-Infrared Absorption

FIR wavelengths are strongly absorbed by water, meaning most FIR energy is captured within the first few millimetres of skin. However, this superficial heating raises core body temperature through thermal conduction and blood circulation, eventually warming the entire body.

Physiological Responses to Infrared Heat

When infrared energy raises your body temperature, several interconnected physiological responses occur:

Cardiovascular Changes

As core temperature rises, your cardiovascular system responds similarly to mild-to-moderate exercise. Heart rate increases (typically to 100-120 bpm during a session), cardiac output rises, and blood vessels dilate (vasodilation). This improved circulation delivers more oxygen and nutrients to tissues while removing metabolic waste products.

Research has shown that regular sauna use is associated with improved endothelial function—the ability of blood vessel walls to dilate and contract properly—which is a key marker of cardiovascular health.

Sweating and Thermoregulation

Your body's primary cooling mechanism is sweating. Sweat glands release fluid onto the skin's surface, where evaporation carries heat away. During an infrared sauna session, you can lose 300-500ml of sweat (or more in longer sessions), triggering significant fluid and electrolyte shifts.

The composition of sweat includes primarily water and sodium chloride (salt), along with small amounts of other minerals, urea, and trace substances. Claims about sweating out "toxins" should be viewed critically—the liver and kidneys, not sweat glands, are the body's primary detoxification organs.

Hormonal Responses

Heat stress triggers the release of several hormones:

• Endorphins: Natural pain-relieving compounds that contribute to the "feel-good" sensation after sauna sessions
• Norepinephrine: A stress hormone that increases alertness and focus
• Growth hormone: Some studies show increased growth hormone release during heat stress, though the magnitude and significance are debated
• Heat shock proteins: Protective proteins produced in response to cellular stress, which may have various health benefits

Infrared vs Convective Heat

A key question is whether infrared heating produces different effects than simply being in a hot room (convective heat). The physics differ:

Convective heat (traditional sauna) heats the air, which then heats your skin surface through contact. Your body must then conduct this heat inward.

Radiative heat (infrared) transfers energy directly into tissue without heating the air significantly. This allows for heating at lower ambient temperatures.

Practically, this means infrared saunas can achieve similar physiological effects—elevated heart rate, sweating, core temperature increase—at lower, more comfortable air temperatures. Whether infrared offers unique benefits beyond this comfort advantage remains an area of ongoing research.

What the Research Shows

Scientific evidence for infrared sauna benefits is growing but still limited compared to traditional sauna research. Here's a balanced summary:

Reasonably Well-Supported

• Relaxation and stress reduction: Heat therapy reliably promotes relaxation
• Improved circulation: Vasodilation during sessions is well-documented
• Pain relief: Multiple studies show benefits for chronic pain conditions
• Muscle recovery: Evidence supports faster recovery after exercise

Promising but Needs More Research

• Cardiovascular benefits: Some studies show improvements in blood pressure and heart function, but long-term data is limited
• Skin health: Near-infrared shows promise for wound healing and collagen production
• Weight loss: Calories are burned during sessions, but effects on long-term weight management are unclear

Overstated or Unproven

• Heavy metal detoxification: Sweat contains trace metals, but significance for health is questionable
• Cancer treatment: No credible evidence supports infrared saunas as cancer treatment
• Immune boosting: Claims exceed current evidence

Optimal Use Based on Science

Understanding the science helps optimise your sauna practice:

Temperature and Duration

Research suggests that core temperature elevation of 1-1.5°C triggers the beneficial cardiovascular and hormonal responses. This typically requires 20-40 minutes in an infrared sauna at 45-60°C. Hotter isn't necessarily better—the goal is sufficient core warming, not maximum environmental heat.

Frequency

Studies showing health benefits typically involve 3-7 sessions per week. The cardiovascular benefits appear to be dose-dependent, with more frequent use associated with greater benefits in Finnish studies of traditional saunas. Whether this applies equally to infrared saunas is still being studied.

Hydration

Fluid loss during sweating can reach significant levels. Pre-hydration, during-session hydration, and post-session rehydration are essential for safety and to support cardiovascular function during sessions.

The Bottom Line

Infrared sauna therapy works through straightforward physics and well-understood physiological responses. When infrared energy heats your body, you experience cardiovascular changes similar to light exercise, release beneficial hormones, and trigger heat adaptation mechanisms at the cellular level.

While some marketing claims venture into pseudoscience, the core benefits of infrared sauna use—relaxation, improved circulation, pain relief, and recovery support—have scientific basis. Used regularly as part of a healthy lifestyle, infrared saunas can be a valuable wellness tool.

For practical guidance on using your sauna effectively, see our first session guide and hydration best practices.