MadSci Network: Physics
Query:

Re: do you get brown from infrared or ultraviolet rays?

Date: Sun Feb 15 21:59:22 2004
Posted By: Adrian E. Popa, Laboratory Director Emeritus
Area of science: Physics
ID: 1076691995.Ph
Message:



Greetings Suzy:

References:
1. NASA's Electromagnetic Spectrum web site:

ht tp://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html

2. What causes Freckles? Mad Science Archives

http: //www.madsci.org/posts/archives/oct98/909788915.An.q.html

3. Melanocyte-Stimulating Hormone (MSH)

http://users .rcn.com/jkimball.ma.ultranet/BiologyPages/

If you search the Mad Science Archives for the terms SUN and TAN you
will come up with many detailed portions of answers to your question.
In this answer I will give you a top level summary of the effect of
electromagnetic energy, including infrared (IR) waves, Visible Light waves
and Ultraviolet (UV) waves, on the human body.

Short Answer

A short answer to your question is that Infrared (IR) waves and visible
light waves cause burning and blistering of the skin. Visible and
Ultraviolet (UV) waves aid each other in the tanning process by producing
hormones and pigment darkening (tanning). However, UV rays can also break
DNA molecules in the skin causing skin damage and possibly cancer.

Detailed Answer

The sun radiates electromagnetic energy at many different wavelengths.
We have given names to the different wavelength portions (bands) of the
Electromagnetic Spectrum. As described in Reference 1, these names are,
ranging from the longest waves to the shortest waves, radio waves,
microwaves, infrared waves, visible light waves, ultraviolet waves, x- rays
and gamma rays. Each of these bands of waves affect the human body
differently.

Electromagnetic waves travel at the speed of light in packets of energy
that we call Photons. The shorter the wavelength of a photon is the greater
is the energy in each photon. Radio photons have enough energy to slightly
vibrate the nucleus of water molecules in the human body and they are used
for Magnetic Resonance Imaging (MRI) of the interior structure of the body.
Microwave photons have enough energy to rapidly vibrate water molecules
and have been used to heat the human body in Diathermy, which is similar
to the heating that occurs in microwave ovens. However, diathermy uses much
less microwave power than is used in an oven. Infrared photons and Visible
Light photons
can burn the human skin and cause a blistering process in which
the surface skin layer is cooked and dies and water forms to protect the inner
skin layers from burning.

As discussed by professor Jim Bridger in Reference 2, Visible light photons
and Ultraviolet (UV) photons interact with electrons in atoms and molecules
in human skin and can cause chemical reactions including the release of
hormones that trigger the darkening of melanin, the black pigment in skin.
Melanin production is controlled by genetics as well as exposure to sunlight.
If a person is dark skinned, then his/her melanocytes are metabolically more
active and make not only more melanin but also a darker variety of the pigment.
When a person is exposed to visible and UV sunlight, the melanocytes are stimulated
to make more melanin. This is the tanning process. Evolutionary biologists
think this process is to protect humans from harmful UV radiation and that
darker skin affords greater protection to dark skinned people. The details of
the Melanocyte-Stimulating Hormone (MSH) process are discussed in
Reference 3.

Ultraviolet (UV) photons can also break up molecules and atoms as can X- rays,
gamma-rays and other ionizing radiation photons and they all have enough
energy to pass through matter while tearing atoms and molecules apart. They
also can be harmful to life. The exposure to UV rays from the sun can damage
the molecular strands in DNA and can cause the strands to break leading to
loss of part of a chromosome. Enough of this sort of damage can lead to skin
cancer (melenoma).

Best regards Your Mad Scientist
Adrian Popa


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