K. B., a 32-year-old fitness instructor, had noticed a "tiny hard lump" at the base of her left nostril while cleansing her face. The lesion had been present for about two months when she consulted a dermatologist. She had recently moved north from Florida, where she had worked as a lifeguard. She thought the lump might have been triggered by the regular tanning salon sessions she had used to retain her tan because it did not resemble the acne pustules, blackheads, or resulting scars of her adolescent years. Although dermabrasion had removed the obvious acne scars and left several areas of dense skin, this lump was brown-pigmented and different. K. B. was afraid it might be a malignant melanoma. On examination, the dermatologist noted a small pearly-white nodule at the lower portion of the left ala (outer flared portion of the nostril). There were no other lesions on her face or neck. A plastic surgeon excised the lesion and was able to reapproximate the wound edges without a full-thickness skin graft. The pathology report identified the lesion as a basal cell carcinoma with clean margins of normal skin and subcutaneous tissue and stated that the entire lesion had been excised. K. B. was advised to wear SPF 30 sun protection on her face at all times and to avoid excessive sun exposure and tanning salons.

K. B.âs basal cell carcinoma may have been caused by chronic exposure to the sun and use of an ultraviolet tanning bed. The scientific explanation for this is the:

a. autoimmune response
b. actinic effect
c. allergic reaction
d. sunblock tanning lotion theory