Infrared and skin: Friend or foe

Abstract

In the last decade, it has been proposed that the sun's IR-A wavelengths might be deleterious to human skin and that sunscreens, in addition to their desired effect to protect against UV-B and UV-A, should also protect against IR-A (and perhaps even visible light). Several studies showed that NIR may damage skin collagen content via an increase inMMP-1 activity in the same manner as is known for UVR. Unfortunately, the artificial NIR light sources used in such studies were not representative of the solar irradiance. Yet, little has been said about the other side of the coin. This article will focus on key information suggesting that IR-A may be more beneficial than deleterious when the skin is exposed to the appropriate irradiance/dose of IR-A radiation similar to daily sun exposure received by people in real life.IR-A might even precondition the skin--a process called photo prevention--from an evolutionary standpoint since exposure to early morning IR-A wavelengths in sunlight may ready the skin for the coming mid-day deleterious UVR. Consequently IR-A appears to be the solution, not the problem. It does more good than bad for the skin. It is essentially a question of intensity and how we can learn from the sun. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: IR-A; Infrared (IR); Irradiance; MMP-1; Photobiomodulation; Photoprevention.

Figure 1

Solar spectrum composition. Red X over UVC means they are blocked by the ozone layer. (NIR: Near Infrared, FIR: Far infrared)

Fig 2

Temperature increase with 970 nm light emitting diode at 80mW/cm² was measured at the derma-epidermal (DE) junction as a function of time (minutes) for a patient. Data monitoring demonstrated that the temperature peaked at 45°C after 15 minutes of irradiation and decreased slowly thereafter[10].

Figure 3

Reduction of MMP-1 levels by ELISA (enzyme-linked immunosorbent assay) in HRS (Human Reconstructed Skin) after LED treatments. A cyclic pattern of alternating highs and lows was observed in response to 11 consecutive treatments (T1–T11) for MMP levels. Values are percent differences ±SEM (n=9) between treated and untreated control HRS samples in mean levels of MMP-1 assessed in the supernatants after each treatment.

Figure 4

Mechanisms of action of PBM. The two principal chromophores are cytochrome c oxidase (CCO) which is unit IV in the mitochondrial respiratory chain, and TRPV ion channels. Photon absorption leads to dissociation of inhibitory nitric oxide from CCO leading to increased enzyme activity and raised ATP production and a burst of reactive oxygen species. The extra ATP produced can activate the Na+/K+ ATPase pump. Another type of calcium ion channel called “transient receptor potential vanilloid” (TRPV) is activated by both visible and infrared light. Calcium signaling is a very important pathway in multiple cell types.

Figure 5

Visible to NIR wavelengths were applied 24h prior to MED 1, MED 2, and MED 3 (Oriel solar simulator) showing reduced erythema in favor of NIR wavelengths.

Figure 6

Ratio of UVR / IR-A solar irradiances, at sea level, with no clouds overhead, as available in the inter-tropics zone (where zenithal sun happens). Calculations were made using the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS), 2.9.5 model, available from NREL and obtained in July 2015 at http://www.nrel.gov/rredc/smarts/about.html.

Figure 7

Early morning (6am) relative irradiance of the sun is higher in the visible and NIR spectrum compared to midday exposure (noon). Calculations were made using the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS), 2.9.5 model, available from NREL (National Renewable Energy Laboratory) and obtained in July 2015 at http://www.nrel.gov/rredc/smarts/about.html.

Figure 8

The solar angle determines the irradiance at different times throughout the day, with a peak at noon (no shadow). The curves represent global solar irradiance for UV-Visible-IR (290-4000 nm) and its IR-A segment (760-1400 nm), as collected on a horizontal surface with no shadow and no clouds. The parameters input into the SMARTS 2.9.5 software are water vapour = 2, ozone = 3, aerosol optical depth at 500 nm = 0.2, and albedo = 0.2. From approximately 8:15 am to 3:45 pm, global sun irradiance climbs above 65 mW.cm⁻². However, IRA irradiance peaks at midday at 35mW.cm^-2 and remains within a safe therapeutic (PBM) range for the length of the day (mean: 20mW.cm⁻²). The dotted lines represent mean irradiances.