Is infrared light harmful to the skin?

Despite its recognised benefits, infrared light is not without risks, particularly in cases of prolonged or high-intensity exposure. The main issue posed by exposure to infrared is the increase in temperature that accompanies it. Indeed, it has been shown that the heat associated with infrared light can stimulate the degradation of collagen by certain matrix metalloproteinases, such as MMP-13, and increase the production of free radicals. As a reminder, free radicals are unstable molecules that react with cellular components, including DNA and dermal support proteins, potentially altering their structure and function. Researchers have notably shown that using a near-infrared light source at 970 nm with an irradiance of 80 mW/cm2 for 15 minutes caused a temperature increase up to 44°C at the dermo-epidermal junction.

Paradoxically, the adverse effects of infrared light appear to counteract its benefits: it could accelerate skin ageing by increasing the production of free radicals and promoting collagen degradation.

What should we understand in this case? In reality, it all depends on the irradiance and the duration of exposure. Irradiance refers to the surface density of energy flux reaching a considered point on a surface and is expressed in W/cm2. As often in biology, there is a bell curve, called "biphasic dose response", which shows that a low dose of infrared generates beneficial responses (cell regeneration, anti-inflammatory effect), while a too high dose becomes harmful (inflammation, tissue degradation). This phenomenon, known as the hormetic effect, underlines the importance of adhering to the recommended protocols for each device.

Several studies have been conducted to test the safety of infrared light as used in dermatology. Notably, the work of Rivkah Isseroff and her team carried out in 2019 can be cited. Two randomised and controlled clinical trials (STARS 1 and STARS 2) were conducted to assess the safety of a high fluence infrared LED (≥160 J/cm²). The participants in the STARS 1 trial had fair skin, while those in STARS 2 had a dark phototype. Both studies involved the administration of red light (633 nm) irradiation 872 mW/cm2 three times a week for three weeks on the inner side of the forearm. An escalation protocol was used, with irradiations from 30 minutes to 2 hours.

No reaction was observed up to a power of 320 J/cm2 (equivalent to 1 hour of exposure) for the participants of STARS 2, and up to 480 J/cm2 (equivalent to 1 hour and 30 minutes of exposure) for the volunteers of STARS 1. The side effects that then manifested included transient erythema, blisters, and slight hyperpigmentation. It thus appears that there is an increased sensitivity to red light in darker skin, justifying precautions and adjustment of doses according to the phototype.

Medical devices and cosmetic tools utilise infrared in a precise manner, with selected wavelengths (≈ 600-900 nm), low irradiances (≈10-50 mW/cm²), and limited exposure times (≈ 15-30 minutes per session) to harness its benefits while minimising the risk of side effects.

Although it is generally safe when used correctly, infrared light requires strict adherence to the usage recommendations provided by manufacturers, particularly in terms of the duration and frequency of sessions. Indeed, as previously explained, excessive exposure could cause tissue damage and lead to redness, blisters or an acceleration of skin ageing. Furthermore, certain contraindications, detailed in the table below, must also be taken into account.