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Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model
Published on: September 7, 2013
Skin pigmentation kinetics after exposure to ultraviolet A
Mette H Ravnbak1, Peter A Philipsen, Stine R Wiegell
1Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, DK-2400 Copenhagen NV, Denmark.
Acta Dermato-Venereologica
|August 19, 2009
Summary
Skin pigmentation response to ultraviolet A (UVA) radiation varies by ethnicity. While fair-skinned individuals show a higher percentage increase, absolute pigmentation gains and time to steady-state are similar across skin types after multiple UVA exposures.
Area of Science:
- Dermatology
- Photobiology
- Skin Physiology
Background:
- Multiple ultraviolet radiation (UVR) exposures are common in nature and phototherapy.
- Previous studies on UVA-induced pigmentation kinetics focused solely on fair-skinned individuals.
Purpose of the Study:
- To investigate steady-state pigmentation and fading kinetics following repeated UVA and UVA1 exposures in both fair-skinned (Scandinavians) and dark-skinned (Indians/Pakistanis) individuals.
- To compare pigmentation responses after 6 and 12 sub-minimal melanogenic doses of UVA and UVA1 radiation.
Main Methods:
- 12 Scandinavians and 12 Indians/Pakistanis received 6 and 12 exposures to broadband UVA and UVA1 on their backs.
- Sub-minimal melanogenic doses were individually predetermined and adjusted for multiple exposures.
- Skin pigmentation was quantified using skin reflectance measurements at 555 and 660 nm.
Main Results:
- The UV dose required for minimal pigmentation was higher in dark-skinned individuals after single broadband UVA exposure but similar after UVA1 exposure.
- Absolute increase in pigmentation was independent of baseline skin type, but percentage increase was higher in fair-skinned subjects.
- 12 exposures led to a higher absolute pigmentation increase and a 2-3 day delay in reaching steady-state compared to 6 exposures; fading took 5-6 months and was independent of skin type.
Conclusions:
- Repeated UVA exposures elicit pigmentation responses that are influenced by both dose and frequency, with absolute gains being comparable across skin types.
- While fair-skinned individuals exhibit a greater relative increase in pigmentation, the time course of pigmentation development and fading is similar between ethnic groups.
- UVA1 radiation shows potential for more consistent melanogenic effects across different skin types compared to broadband UVA.
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