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Relationships
between skin phototype and pigment index, surface corneocyte melanin
content and measured UV sensitivity.
Edwards, Chris1
Royal Gwent Hospital, Newport, South Wales, UK 1
Abstract-
While constitutive skin pigmentation should have an influence on phototype,
this is not an explicit criterion for types I to IV. Phototype has been
compared to measured skin pigmentation in two ways. Using a two-wavelength
diffuse reflectance spectrophotometric device (Melanin meter, Dermotronics,
Cardiff - now Mexameter, Courage & Khazaka, Germany) the melanin pigment
index of a group of mixed skin colour subjects was compared to skin
phototype. While, as expected, the mean melanin index increased with
increasing phototype there was not a linear relationship. Much overlap
occurs between phototypes, and differences in pigment index between
adjacent phototypes are not statistically significant. Melanin granule
content of surface corneocytes was measured histologically in skin types
II to VI. A strong positive correlation between phototype and melanin
content was measured (r=0.95 in sun exposed areas, r=0.89 in unexposed
areas, Spearmans Rank test). Also, the number of corneocytes with a
distribution of granules around the nucleus (Nuclear caps) was strongly
dependant on phototype. Thus phototype has some relationship to both
constitutional and facultative pigmentation. The South Wales population
is mainly types I to IV. In our photodermatology clinic, phototype I
is an exclusion criterion for phototherapy. We do not routinely measure
MED or MPD from skin types V and VI. In a group of 186 patients with
both measured MED or MPD and an ascribed phototype, there is an obvious
influence of phototype on measured sensitivity. However, the variability
in measured sensitivity within each phototype makes prediction of sensitivity
from phototype alone impossible. Additional factors such as eye and
hair colour and measured pigmentation at the time of presentation may
improve the predictive value of skin phototyping.
Keywords: Phototype,
pigmentation, corneocyte pigmentation, UV sensitivity
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