II / 40
UVA
Tans skin by changing the color of
“melanin” through oxidization Pigmentation
Faint tanning of skin = 1 MMD
(Minimal Melanogenic Dose)
Over a century ago it was discovered that
invisible light rays in the ultraviolet region of
the light spectrum caused the skin to
darken. As scientists studied ultraviolet light,
they divided this region into three groups,
UVA (320-400 nm), UVB (280-320 nm) and
UVC (200-280 nm). Nanometers, or nm for
short, define the wavelength of the
ultraviolet light; one nanometer is about
1/100,000 the thickness of a human hair.
The primary effect of UVA light on the skin
is called pigmentation, or darkening of the
skin. The primary effect of UVB on the skin
is called erythema, or reddening of the skin.
UVB
Reddens skin (erythema) and forms
“melanin” in the skin (Melanogenesis)
Faint reddening of skin = 1 MED
(Minimal Erythema Dose)
How
We
Tan
Erythema begins shortly after exposure to UVB, and varies
depending upon the intensity and length of the exposure. How much
redness is also determined by how much UVB is coming from which
wavelengths; for example, UVB at 290nm produces 100 times more
erythema than UVB at 320nm. At the same time as erythema
is taking place, the UVB causes melanin to form just beneath the
surface of the skin. The melanin is oxidized and turned brown by the
UVA rays given off by the tanning lamps.
Thus, the tanning process involves the relatively quick reddening of
the skin, followed by a slower forming, but longer lasting browning of
the skin. Without some exposure to UVB rays, the tanning process
cannot take place. The key is providing sufficient amounts of UVB to
properly stimulate melanin, followed with effective amounts of UVA
to complete the tanning process.