Biomedical Engineering Reference
In-Depth Information
skin can develop redness due to vasodilation, swell, become painful, or even
blister if the dose of light is su
ciently large. Somewhat after these changes
occur, in 2-7 days, tanning and stratum corneum thickening occur. Those
individuals who have very little capacity to tan will not produce much extra
melanin after UV exposure, but will still produce thickening of the stratum
corneum [9]. The time course of the acute changes resulting from UV exposure
is also dependent on the dose of light. Doses of light that are in large excess
of the photoprotective capacity of an individual's skin will result in much
more long-lasting and intense erythema [9]. Thus, the changes produced in
skin are very dependent on the genetic capacity for melanin synthesis, which
is termed the skin type [25]. Skin types are rated on a scale of 1 through
6 (Fig. 16.3). Individuals with type 1 skin always burn and never tan when
exposed to UV light. Individuals with type 2 skin burn initially, but then can
tan modestly after recurrent exposure to light. Those with type 3 skin may
burn initially in the spring, but will reliably tan thereafter. Those with type 4
skin have significant coloration without sun exposure, and always tan readily.
Those with type 5 skin have deep coloration without sun exposure, but tan-
ning is evident after sun exposure. Lastly, individuals with type 6 skin have
constant very deep pigmentation in which tanning is di
cult to detect. Light-
related skin cancer is prevalent primarily in skin types 1-3. Over the course of
years, recurrent exposure of individuals to UV light produces chronic changes
in susceptible, light skinned, individuals. Most evident is photoaging. Char-
acterized by deep wrinkling, uneven pigmentation, vascular dilatation, and
hyperkeratotic changes in epidermis, photoaging is what most people think
Fig. 16.3.
Skin types: capacity to tan, burn, and risk of skin cancer
