Seborrheic keratosis in the Korean males: causative role of sunlight.

BACKGROUND/PURPOSE: Seborrheic keratoses (SKs) are common epidermal tumors in the white population over 40 years. The etiology of SKs is not well known; however, exposure to sunlight was suggested to play a role in the development of them. To our knowledge, no well-designed study has been undertaken in order to investigate the clinical characteristics of SKs in a brown-skinned Korean population. The aim of this study was to assess the prevalence and clinical features of SKs in the Korean males and to investigate the possible relationship of SKs with sun exposure and possible risk factors of developing SKs.

METHODS: A total of consecutive 303 male volunteers, aged 40-70 years, were recruited from general community and public health centres. Each volunteer was interviewed regarding demographic data, sunlight sensitivity, lifetime cumulative sun exposure and smoking history. Skin examination was performed except for scalp, buttocks and genitals. All SKs were recorded about the anatomical distribution, the size of each lesion measured with a caliber, color and morphology.

RESULTS: The mean overall prevalence of SKs in the Korean males, aged 40-70 years was 88.1%. A considerable increase in the prevalence of SKs was shown from 78.9% at 40 years to 93.9% at 50 years and 98.7% in those over 60 years. The mean number of lesions per person was 5.5 at 40 years, 9.2 at 50 years and 13.4 at 60 years. Seborrheic keratoses were considerably more frequent on exposed areas (0.47 +/- 0.06/percentage of body surface area, BSA) than partly exposed areas (0.04 +/- 0.01/percentage of BSA). The majority of lesions were concentrated on the face (0.98 +/- 0.09/percentage of BSA) and on the dorsum of each hand (0.51 +/- 0.08/percentage of BSA). The size of each lesion on exposed areas also became significantly larger by decade significantly (P < 0.01). The estimated area covered by SKs per percentage of BSA on exposed areas was 5.7-fold larger than that on partly exposed areas at 40 years, 11.2-fold larger at 50 years and 18.3-fold larger at 60 years. Aging by decade showed a 2.08-fold increased risk for SKs (n > or = 6) (95% CI, 1.07-4.08) at 50 years and a 3.47-fold risk (95% CI, 1.67-7.20) at 60 years on exposed areas compared with the 40-year age group, for developing many SKs (n > or = 6). Lifetime cumulative sunlight exposure of more than 6 h per day was associated with a 2.28-fold higher risk of SKs than a sun exposure of less than 3 h per day. A tendency for an odds ratio value reduction was found on increasing Fitzpatrick skin types I-III to VI, V; however, this was without statistical significance.

CONCLUSIONS: Seborrheic keratoses are common in the Korean males, aged 40-70 years, and may be a major pigmentary problem. Both aging and cumulative sunlight exposure were found to be independent contributory factors.