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Vancouver,
BC--Topical antioxidant formulations should be considered supplemental
to sunscreens, and may even offer better sun protection than sunscreens,
said Sheldon R. Pinnell, MD, professor emeritus of dermatology,
Duke University Medical Center, Durham, NC.
Dr. Pinnell is a consultant for Dallas, TX-based SkinCeuticals which
distributes skin care products exclusively through physicians and
licensed healthcare professionals.
Speaking at Dermatology Update 2004, Dr. Pinnell described his research
laboratory's recent experiments applying topical antioxidant or
vehicle to pig skin.(1, 2)
Pig skin was used because it is most like human skin and allows
researchers to obtain the multiple observations required to achieve
statistical significance.
In the first set of experiments, an aqueous solution of 15 per cent
L-ascorbic acid and 1 per cent alpha-tocopherol was applied to the
skin for four days. Then the skin was irradiated with light using
a solar simulator.
On Day 5, erythema, sunburn cells, and thymine dimers were measured
and compared to vehicle.
In a second set of experiments, an aqueous solution of 15 per cent
L-ascorbic acid, 1 per cent alpha-tocopherol, and 0.5 per cent ferulic
acid was used.
Results
Colorimetric tests show that vitamins C and E combined with a stabilizing
plant antioxidant called ferulic acid offer eight-fold protection
against solar-simulated light compared to vehicle.(2)
The combination
of Cand E alone provided four-fold protection.(1) Polarized photographs
of skin measured by colorimeter showed that erythema was reduced.
Skin biopsy showed that sunburn cells were reduced, and antibody
testing showed that thymine dimers were reduced.
Skin penetration
The secret to getting L-ascorbic acid and alpha-tocopherol into
skin is to formulate the mixture at a pH lower than 3.5, where the
pure compounds are not ionized, Dr. Pinnell said. Once in the skin,
the topical antioxidant has a half life of four days, which means
that the antioxidants stay in the skin where they can work to neutralize
free radicals. This is different from a sunscreen, which must be
applied prior to sun exposure and be reapplied regularly.
Can't sunscreens do it all?
A 2003 paper in the Journal of Investigative Dermatology claimed
that the UVA/free-radical protection currently provided by sunscreens
is inadequate.(3) It was reported that high-factor sunscreens block
only 55 per cent of free radicals generated in skin when applied
directly to the skin at the recommended amount of 2 mg/cm2 (which
is how the FDA measures SPF)), and even less at lower application,
suggesting that sunscreen users are little protected against the
damaging free radical effects of UVA.
As well, consumers applying a product containing an SPF 30 as it
is typically applied (0.5 mg/cm2), may only receive protection equivalent
of an SPF 3 or 4 (or threefold to fourfold protection) because they
do not apply enough of the product.(4)
SkinCeuticals expanded into Canada in the summer of 2004, and is
marketing its products through the Toronto-based Nordic Selfcare
Institute. Tel: 416.764.7737 or 1.888.201.1875.
1. Lin, Jing-Yi, et al, J Am Acad Dermatol 2003;48:866-74
2. Lin Jing-Yi., et al, J Invest Dermatol 2004,122:883
3. Haywood, R. et al, J Invest Dermatol 2003;121:862-868
4. Wulf, H.C. et al, Photodermatol, Photoimmunol, Photomed 1997:13:129-132
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