Photoprotection

Last updated: 6 February 2010.

Introduction

PhotoprotectionPhotoprotection is protection from light and ultraviolet radiation. E.g. Melanin provides natural photoprotection, whilst sunscreens provide artificial photoprotection. Click here for more information. describes the act of protecting against light and in particular ultraviolet radiationUltaviolet (UV) radiation is emitted by the sun, and is a region in the electromagnetic spectrum between 400-200nm, that can be broken down into three categories: UVA which is between 400-320nm, UVB which is between 320-280nm, and UVC between 280-200nm. Click here for more information. (UVR). Ultraviolet radiationUltaviolet (UV) radiation is emitted by the sun, and is a region in the electromagnetic spectrum between 400-200nm, that can be broken down into three categories: UVA which is between 400-320nm, UVB which is between 320-280nm, and UVC between 280-200nm. Click here for more information. is emitted by light sources, most commonly from the sun and sun beds, and can be broken up into three regions based on their wavelength: UVA, UVB,and UVC. UVC is mostly absorbed by the atmosphere before it reaches the Earth's surface and poses no risk to life. UVA and UVB both reach the Earth's surface and may cause skin damage, such as accelerated skin ageing and, more importantly, may induce DNA mutations leading to skin cancers. Skin cancer affects animals and humans. To survive in our mostly sun drenched planet, organisms have adapted natural defense mechanisms against ultraviolet radiationUltaviolet (UV) radiation is emitted by the sun, and is a region in the electromagnetic spectrum between 400-200nm, that can be broken down into three categories: UVA which is between 400-320nm, UVB which is between 320-280nm, and UVC between 280-200nm. Click here for more information..

Natural photoprotection

Humans have developed a natural photoprotectivePhotoprotection is protection from light and ultraviolet radiation. E.g. Melanin provides natural photoprotection, whilst sunscreens provide artificial photoprotection. Click here for more information. system that protects cellular DNA from the harmful UV radiationUltaviolet (UV) radiation is emitted by the sun, and is a region in the electromagnetic spectrum between 400-200nm, that can be broken down into three categories: UVA which is between 400-320nm, UVB which is between 320-280nm, and UVC between 280-200nm. Click here for more information. emitted from the sun. PhotoprotectionPhotoprotection is protection from light and ultraviolet radiation. E.g. Melanin provides natural photoprotection, whilst sunscreens provide artificial photoprotection. Click here for more information. is mostly offered by biological chromophores, chemical groups of molecules that are capable of selective light absorption. Some of the organic compounds found in man are DNA, urocanic acid, amino acids, melaninMelanin is a naturally produced polymer found in a multitude of locations in the body, from the eye and ear, to the brain and skin. Click here for more information. precursors and eumelanin.

Skin biometrics offers the opportunity to assess spectroscopic measurements. Various factors, such as solubility of the chromophores determine the ability to assess the individual absorption spectra and scattering properties of human tissue.

Hemoglobin and melaninMelanin is a naturally produced polymer found in a multitude of locations in the body, from the eye and ear, to the brain and skin. Click here for more information. are the main chromophores in the visible range of the electromagnetic spectrum (460-560 nm).

Photoprotection in humans

The absorption of light by an object is directly correlated to the incident radiation and the absorption coefficient (AC) of the object, and in skin characterized by its chromophore concnetration. Chromophores are also referred to as quenchers of photoexcited states (QPES), by quenching or dissipating the energy transferred from sunlight to the dermis. The main chromophores of human skin are hemoglobin, melanin and water. Hemoglobin shows a high molar extinction coefficient in the “blue” region of the spectrum (405-450 nm) in human skin.  Eumelanin sees a drop in its absorption curve from 200 to 70 nm, making its absorption most important in the “blue” band around 400 nm. Water has a very low AC below 800 nm.
Traditionally, reflectance spectroscopy has been used to determining chromophore concentrations and absorbing molecules in human skin at various wavelengths. It has been found that the wavelength dependence of the scattering coefficient of skin remains relatively constant among individuals.

By using the entire visible spectrum to assess chromophore concentration of e.g hemoglobin  and melanin, the method becomes less sensitive to minor reflectance fluctuations. Furthermore, this method can be applied to any added chromophore with known absorption properties which is present in sufficiently high concentrations to perturb the reflectance spectrum.

Advanced techniques to map individual chromophores are referred to as cutaneous optics, mathematical models to explain the interaction of sunlight with skin using spectrophotometric analysis. Another recent technique makes use of spectrophotometric intracutaneous analysis (SIA) measure in vivo the concentration and distribution of eumelanin, oxyhemoglobin, and dermal collagen to produce concentration maps of these chromophores (SIAscopy).
 

References

• Lim, H W & Soter, N A (2001). Clinical Photomedicine. CRC Publishing.
• Matts, P J (2008). "New Insights into Skin Appearance and Measurement." Journal of Investigative Dermatology Symposium Proceedings. Vol 13, pp 6-9.
• Shimada, M et al (2001). "Melanin and blood concentration in a human skin model studied by multiple regression analysis: assessment by Monte Carlo simulation." Phys. Med. Biol. Vol 46, pp2397-2406.
• Stamatas, G N, Zmuzdka, B, Kollias, N & Beer, J (2004). "Non-invasive measurement of skin pigmentation in situ." Pigment Cell Research. Vol 17 (6), pp618-626.
• Walker, S L & Young, A R (2007). "An action spectrum (290–320 nm) for TNFα protein in human skin in vivo suggests that basal-layer epidermal DNA is the chromophore." Proc Natl Acad Sci. Vol 104 (48).
• Zonios, G, Bykowski, J & Kollias, N (2001). "Skin Melanin, Hemoglobin, and Light Scattering Properties can be Quantitatively Assessed In Vivo Using Diffuse Reflectance Spectroscopy." Journal of Investigative Dermatology. Vol 117, pp1452-1457.
  

Resources

• The physiological "UV tanning response", original thoughts on UV and pigmentation. Clinuvel Technology Update, February 2010.