Steven Q. Wang - Principles and Practice of Photoprotection

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Part I

Springer International Publishing Switzerland 2016

Steven Q. Wang and Henry W. Lim (eds.) Principles and Practice of Photoprotection 10.1007/978-3-319-29382-0_1

1. Clinical and Biological Relevance of Visible and Infrared Radiation

Kelsey Lawrence 1

(1)

Department of Dermatology, Henry Ford Hospital, 3031 W. Grand Blvd., Suite 800, Detroit, MI 48202, USA

Kelsey Lawrence

Email:

Mohammed Al-Jamal

Email:

Indermeet Kohli

Email:

Iltefat Hamzavi (Corresponding author)

Email:

Keywords

Visible Infrared Radiation Light Laser Photoprotection

Key Points

• Biologically, visible radiation has been shown to induce erythema, pigmentation, free radical production, and DNA damage, while infrared radiation has been shown to induce erythema, thermal pain, photoaging, cytotoxicity, DNA damage, and oxidative stress.
• Visible light has been shown to be an action spectrum in solar urticaria, chronic actinic dermatitis, and porphyrias; it is used for the treatment of hyperbilirubinemia. Infrared radiation can cause erythema ab igne and squamous cell carcinoma.
• Lasers with wavelengths in the visible and infrared spectrum can be used to treat vascular and pigmented lesions, keloids, etc. IPL, LLLT, and PDT are other light sources with wavelengths in the visible and infrared spectrum that are also used to treat numerous dermatologic conditions.
• New imaging techniques that use visible and infrared radiation have been recently developed. The data is promising and could greatly impact the field of dermatology in the future.
• Active research is ongoing on effective photoprotective measures against visible light and infrared radiation.

1.1 Introduction

The sun emits electromagnetic radiation encompassing a wide range of wavelengths (Table ]. It should be noted that in the UV spectrum, only UVB and UVA reach the surface of the earth; UVC is filtered out completely in the hemisphere. There has been extensive research into the effects of UV radiation on the skin, but until recently there has not been much research on the effects of visible and infrared radiation on the skin. This chapter will discuss the biological and clinical relevance of visible and infrared radiation.

Table 1.1

Electromagnetic spectrum and corresponding wavelengths

Light spectrum	Wavelength
Gamma ray	less than 0.01 nm
X-ray	0.0110 nm
Ultraviolet	10400 nm
UVC	200290 nm
UVB	290320 nm
UVA	320400 nm
Visible	400700 nm
Violet	400450 nm
Blue	450495 nm
Green	495570 nm
Yellow	570590 nm
Orange	590620 nm
Red	620700 nm
Infrared-A	7001400 nm
Infrared-B	14003000 nm
Infrared-C	3000 nm 1 mm
Microwave	1 mm1 m
Radio	1 mm100 km

Electromagnetic radiation is made up of photons, which have the properties of both waves and particles. When photons reach the surface of the skin, they can be reflected, scattered, absorbed, or transmitted. Reflection occurs at the skin surface and can be used for diagnostic purposes but is not useful therapeutically. Scattering is altering the direction of light transmission and also affects the depth of penetration. Most of the scattering of light is done by the collagen that is present in the dermis. However, scattering is also dependent on the wavelength, with shorter wavelengths undergoing more scattering compared to longer wavelengths [].

In order for a photon to exert a clinical effect, it must be absorbed. Molecules in the skin that absorb photons are called chromophores. Absorption is dependent on the depth of penetration of the radiation and the wavelength absorbed by the chromophore. The depth of penetration into the skin varies with wavelength; the longer wavelengths penetrate deeper than shorter wavelengths. Therefore, blue light, which is at the shorter end of the wavelength spectrum of visible light, can be used clinically for lesions contained in the epidermis, while red light, which has a longer wavelength, is useful for thick lesions or to target deeper structures [].

A variety of molecules can act as chromophores, some examples being amino acids, lipids, porphyrins, photosensitizing drugs, DNA, hemoglobin, bilirubin, melanin, and water. When a chromophore absorbs a photon, the chromophore transitions to an excited state, transiently. The chromophore releases energy, in the form of heat or light, when it returns to the ground state. The chromophore can then transfer this energy to another molecule or undergo chemical changes. Multiple photons are necessary to produce sufficient energy to cause cellular changes, which then leads to a clinical effect [].

1.2 Visible Spectrum

Visible light is the portion of the electromagnetic radiation responsible for general illumination and is visible to the human eye. The wavelength of the visible radiation spectrum is from 400 to 700 nanometers (nm). Each color of light represents a different wavelength, with blue being at the shorter end of the spectrum and red at the longer end (Fig. for more details on specific wavelengths.

Fig. 1.1

The wavelengths and their corresponding depth of penetration in the skin of each band within the visible and infrared spectrum

1.2.1 Biological Effects

1.2.1.1 Erythema

Erythema is a cutaneous inflammatory reaction and can be associated with warmth and tenderness; blisters can form if severe. Erythema during or immediately after sun exposure can occur transiently in fair skin types. Delayed erythema occurs in all skin types, with a peak occurring between 6 and 24 h after exposure [].

Erythema is mostly caused by UVB radiation. However, UVA radiation, primarily UVA2 (320340 nm), can contribute to skin erythema, and visible light has been shown to induce transient erythema [].

Skin type plays a role in the timing and intensity of erythema from visible radiation. Mahmoud et al., using a light source that emits 98.3 % visible light, found that visible light can induce erythema, in individuals with Fitzpatrick skin types IVVI, immediately after exposure, surrounding the area of immediate pigment darkening. However, the erythema started to fade 30 min later and was completely gone in 2 h. Of note, they were unable to induce any erythema in skin type II individuals even at the highest dose tested, 480 J cm2. The authors proposed a possible thermal effect from the reaction within the chromophores causing vasodilation and therefore erythema. They also proposed that the increased melanin concentration, one of the chromophores with absorption in the visible light spectrum, in the darker skinned individuals could account for the increased heat production and therefore the increased erythema that occurred in darker skin types [].

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