Skin biopsy specimens were fixed in 10% neutralbuffered
formalin and processed for routine histology.
Hematoxylin-eosin–stained center-cut sections
of each biopsy specimen were analyzed for sunburn
cells (keratinocytes with pyknotic nuclei having an
eosinophilic cytoplasm). The entire 8-mm center
section of the histologic ribbon was analyzed and
the results expressed as sunburn cells/mm. When
photodamage is extensive, it may be difficult to
precisely define a sunburn cell in the presence of
epidermal necrosis. For analysis, whenever sunburn
cells could not be accurately identified, an upper
limit of 35 sunburn cells/mm was used.