We love the sun. We complain about rainy days, we look forward
to summers at the beach. But we hate sunburns, wrinkled skin,
and melanomas. All of those nasty things are the result of the
ultraviolet that comes with the warmth and light of sunshine.
There are a large number of chemicals used to block ultraviolet light,
either to protect the user's skin, or to protect a product from being
damaged (colors fading, scents decomposing, etc.)
Some are vitamins, such as
Some are opaque powders used in
creams, such as zinc oxide, or titanium oxide. Others are designed
to be invisible (they don't block visible light) like
There are two ways to protect the skin from ultraviolet light --
absorb the light, or reflect the light. Zinc oxide and titanium
oxide reflect, or scatter light of many frequencies, from infrared
through ultraviolet. That is why they appear opaque white.
When you don't want to paint yourself white, you can paint yourself
with a color that absorbs ultraviolet, but is transparent to visible
Ultraviolet light is often divided into two types, UV-A, which has
a longer wavelength (320-360nm) and UV-B, which has a shorter
wavelength (280-320nm). Shorter wavelengths mean higher energies.
UV-B is more damaging than UV-A. Some UV blockers are optimized
to block the shorter wavelengths, while letting the longer wavelengths
get through. SPF numbers (sun protection factor) only describe
UV-B protection. A high SPF can still let UV-A through. UV-C
is the shortest wavelength of ultraviolet light, but it is effectively
screened out by the ozone layer of the atmosphere.
UV-B causes sunburn, but UV-A damages collagen (connective tissue)
and blood vessels, causing aging effects such as wrinkled skin.
Sunscreens block the body's ability to make Vitamin D from sunlight.
If you are using sunscreen a lot, or do not get much sun, getting
supplemental Vitamin D in your diet may be a good idea.
Because governments only allow certain percentages of each UV
absorbing compound, the higher SPF formulations generally have
several UV absorbers in them.
For a more in-depth discussion of how sunscreens work, see the
Chemistry lesson at the end of the section on