Biomedical Engineering Reference
In-Depth Information
Fig. 16.6.
The sensitivity of an individual to damage from sun exposure is measured
by determining their minimal erythema dose. The least amount of light capable of
producing a clearly outlined spot of redness, (termed erythema) is called the minimal
erythema dose for that individual. The amount of light required to produce erythema
varies nearly 100-fold because of the differences in constitutive skin color
the sun protection factor, or SPF. For instance, if a garment has an SPF of
15, then an individual who ordinarily develops erythema after 10 min of light
exposure without protection will now be able to tolerate 150 min of exposure
when wearing the garment [9].
Use of sunscreens as a method of protection from skin cancer risk has
been actively debated in recent years. There is definitive evidence that their
use protects animals from skin cancer in the laboratory. Similar trials have
not been conducted in humans, but there is strong supportive evidence. Some
debate has arisen about whether sunscreens may interfere with Vitamin D
metabolism, but it is clear that the amount of Vitamin D needed can be
readily obtained from dietary sources. In addition, very little light is needed to
produce Vitamin D from endogenous sources. It would be the rare individual
who could be su
ciently assiduous in their sun protective measures to produce
Vitamin D deficiency.
Most currently available sunscreens were initially formulated to protect
against UVB wavelengths, from 280 to 320 nm. There are two major classes
of these compounds: UVB absorbing and physical sunscreens [9]. With recent
rapid advances in material science, many new sunscreen compounds are being
created and tested. Some of these new sunscreens have already been tested
for safety and met standards for European approval, while some aspects of
safety for new sunscreen materials are still being evaluated.
Physical sunscreens are effective across a broad range of wavelengths. They
are made up of particulates that can scatter and reflect UV light. In general,
they contain zinc oxide, titanium dioxide, magnesium oxide, talc, or kaolin
(up to 25%). Sunscreens in this category provide the best block available in
