Fifty-six mice were classified into four groups; Group A (control group, n=8), Group B (exposure group, n=16), Group C (n=16) treated with sunscreen 15 minutes before UVB irradiations and group D (n=16) sunscreen treated 60 minutes before UVB exposure. Mice were irradiated 30 minutes 5days/week (12 weeks), and group C-D treated five days/week (12 weeks). Skin samples were taken in the mid and end of the experiment. The result of this study revealed that, epidermal thickness in group A was 7.155µm. At the mid-period of the experiment, severe epidermal hyperplasia was observed in group B with epidermal thickness 118.712µm, while in group C and D mild to moderate epidermal hyperplasia were noted with decreasing epidermal thickness to 64.154 and 90.042µm respectively. At the end of the experiment in Group B epidermal thickness reached to 281.35µm with seborrheic keratosis development, whereas in group C and D totally inhibited the development of seborrheic keratosis and epidermal thickness decreased again into 42.347 and 55.915µm. In conclusion, chronic UVB radiation-led to epidermal hyperplasia and seborrheic keratosis, sunscreen prevented the development of seborrheic keratosis and decreased the UVB-induced epidermal hyperplasia.

Key words: Epidermal hyperplasia, Epidermal thickness, Seborrheic keratosis, Sunscreen, UVB