Regular use of
sunscreens has increasingly been recommended to
prevent the long-term effects of sun exposure --
including the development of skin cancers -- despite
insufficient data on the efficacy of this practice.
Researchers in Australia performed a randomized,
controlled trial of the effect of daily use of a
broad spectrum sunscreen on solar keratosis.
Five hundred
eighty-eight subjects who each had at least one
solar keratosis applied either sunscreen containing
methoxycinnamate and dibenzoylmethane with an SPF of
17 (which blocks 94% of radiation in the 290 to 320
nm wavelengths and 90% of radiation in the 320 to
360 nm wavelengths) or a base cream once a day
during the 7 sunniest months of the Australian
spring and summer. Subjects were advised to avoid
the sun and to protect themselves with hats and
clothing. Three times during the 7 months subjects
were examined for the development of new solar keratosis
and the disappearance of previously
existing ones. Four hundred thirty-one subjects
completed the study.
During the study
period, the mean number of solar keratosis increased
by 1.0 per person in the base-cream group and
decreased by 0.6 per person in the sunscreen group.
Fewer new lesions appeared in the sunscreen group
than in the base-cream group, with a rate ratio of
0.62. Of the lesions present at baseline, 25%
disappeared in the sunscreen group, as compared with
18% in the base-cream group; after correcting for
sex and skin type, the likelihood of remission was
1.53 times greater in the sunscreen group. The
development of new lesions and the remission of
existing ones correlated in a dose-response
relationship with the amount of sunscreen used.
Comment:
These results suggest that regular use of broad
spectrum sunscreens is at least partially successful
in preventing the development of
solar keratosis,
the precursor lesions of nonmelanoma skin cancer. By
extrapolation, it seems reasonable to conclude that
long-term, appropriate sunscreen use will prevent
the development of nonmelanoma skin cancer. These
investigators have previously shown that solar keratosis disappear spontaneously, especially in
persons who reduce their exposure to sunlight.
Combining sunscreen use with sun avoidance appears
to both reduce the number of existing solar keratosis and decrease the development of new
lesions. This information is of great practical
significance for public health prevention and can be
used by dermatologists in efforts to convince
patients to limit sun exposure and increase
sunscreen use.
