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TPDN 1989, Vol. 49, No. 24
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LIMITATIONS OF SUNSCREEN USE
Sunscreens are designed to either act as a barrier
to sun (eg, titanium dioxide) or to absorb sunlight
in the wavelength region (290-320 nm) consid-
ered to be responsible for skin cancers. The most
popular of the latter type is para-aminobenzoic
acid (PABA).4 A grading system is in place that
rates sunscreens according to their sun protec-
tive factor (SPF). This represents the ratio of
the minimal ultraviolet dose needed to produce
erythema 24 hours after exposure with and
without sunscreen. The ability of sunscreens to
prevent cancers has been demonstrated experi-
mentally in animals. Their effectiveness, how-
ever, has not been shown in human studies due to
the difficulty in replicating conditions encoun-
tered by human users.5
Sunscreen effectiveness depends mainly on proper
application. A study was conducted involving 50
regular users of sunscreen with previous solar
skin damage, a group expected to be highly
motivated. It was found that many sun-exposed
areas such as eyebrows, ears, behind the ears,
hands, and neck were not protected on a daily
basis. In addition, sunscreen effectiveness is also
limited by other factors such as heat, wind,
humidity, perspiration, and water exposure.5
The risk of skin cancer could conceivably in-
crease if individuals apply sunscreens improp-
erly and depend on the sunscreen for protection
while increasing their sun exposure.
The most effective preventive measures are
avoiding excess sun exposure and using sun
barriers such as clothing and hats. The proper
application of sunscreen is necessary for maxi-
mal effectiveness. This includes the n nnl i .n tion
of sunscreen to all sun-exposed parts and fre-
quent reapplication, especially after swimming
or physical activity.
EARLY DETECTION
Early detection of malignant melanoma is impor-
tant to increase the individual's chance of
survival. Melanomas often begin as growths
similar to moles that grow in size, change color,
become ulcerated, and bleed easily when injured.
Malignant melanoma can rapidly metastasize,
but is curable if detected early and given proper
treatment. Individuals should be reminded of
the warning signs of melanoma which include:
an asymetrical mole, where one half does not
match the other; ragged, notched, or blurred
edges; nonuniform pigmentation; a sudden or
continuing increase in the size of a mole.
Exposure to ultraviolet radiation is the most
important risk factor for malignant melanoma.
The evidence suggests that reduction of unpro-
tected sun exposure could substantially reduce
morbidity and mortality from both malignant
melanoma and other forms of skin cancer.
References:
1. American Cancer Society, Cancer facts and figures - 1987.
2. Stern RD, Weinstein MC, Baker SG. Risk reduction for non-
melanoma skin cancer with childhood sunscreen use. Arch
Dermatol 1986;122:537-45.
3. Johnson EY, Lookingbill DP. Sunscreen use and sun exposure:
trends in a white population. Arch Dematol 1984;120:727-31.
4. Osgood PJ, Moss SH, Davies DJ. The sensitization of near-
ultraviolet radiation killing of mammalian cells by the sun-
screen agent para-aminobenzoic acid. J Invest Derm 1982;
79:354-7.
5. Watson A. Sunscreen effectiveness: theoretical and practical
considerations. Aust J Derm 1983;24:17-22.
TEXAS PREVENTABLE DISEASE NEWS (ISSN 8750-9474) is a free, weekly publication of the Texas Department of
Health, 1100 West 49th Street, Austin, TX 78756. Second-class postage paid at Austin, TX. POSTMASTER: Send
address changes to TEXAS PREVENTABLE DISEASE NEWS, 1100 West 49th Street, Austin, TX 78756.
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