MadSci Network: General Biology
Query:

Re: Does Red light from sunlight have an impact on our skin-tone?

Date: Wed May 2 16:41:28 2012
Posted By: Mike Klymkowsky, Professor
Area of science: General Biology
ID: 1330301231.Gb
Message:

skin and light


You ask some very interesting questions. First, it is worth knowing that skin and hair color is determined by only a few factors in humans.  These include the amount and distribution of eumelanin pigment (black-brown), phenomelanin (red-yellow and restricted largely to hair), carotenes (yellow), as well as the presence of oxygenated hemoglobin (red) and deoxyhemoglobin (blue) in blood vessels in the skin. 

Melanin is the most important of these.  Melanin is organized in cytoplasmic granule; their size, number, and intracellular arrangement is a primary determinant of skin (and hair) color (for a review see this paper  by Quevedo et al., 1985).   

 

People have studied how light passes through (or rather into) skin. 

 

  light
 

They found that longer (redder) wavelengths of light (you were right) go further into the skin than bluer and ultraviolet light.  The graph above is taken from a paper that measured this directly (see Bachem & Reed, 1931). 

It is worth noting that red light does not have enough energy to break bonds in DNA (genes).  This is one reason it enters further into the skin, it is not absorbed by the molecules that make up the skin.  It could warm, but not damage skin cells (or the molecules within them). 

The problem with blue (and ultraviolet) light (and why it does not penetrate the skin very well) is that the shorter the wavelength of light (blue and particularly UV have shorter wavelengths than infrared or red), the more energy it contains. 

The more energy, the more likely it is that if the light is absorbed by a molecule (like DNA) the more likely that it will break a bond, leading to damage (and in the case of DNA mutation). It is the UV light from the sun that causes tanning, sun burn, and eventual skin cancer.   

That said, there are people with blue skin (see this link), although this appears to be due to a disease (often poisoning), known as methemoglobinemia

 

 


Be a biofundamentalist™ and Socratic


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