Objective To clarify the relationship of p63 and CD44 expressions with age and ultraviolet irradiation in the process of skin aging.Methods Full-thickness skin samples were obtained from the normal skin at different sites,including 44 sun-exposed sites(face,neck,dorsal aspect of the forearm),46 sun-protected sites(abdomen,thigh),and 31 semi-exposed sites(back,flexor aspect of the forearm,upper arm,leg),of 121 volunteers(63 males and 58 females).Of all the volunteers,55 were 10 t0 30 vears of age (young),41 were 31 to 50 years of age(adult),and 25 were 51 to 79 years of age(old).Immunohistochemisty using antibodies to p63 and CD44 was applied to detect the expression of p63 and CD44 in these specimens.Imaging analysis software was utilized to calculate the percentage of p63-expressing cells in basal layer as well as the expression level of p63 and CD44.Results In stratum basale,the percentage of p63-expressing cells decreased with age(r=-0.218,P＜0.05),but showed no significant difference among sun-exposed skin,semi-exposed skin and sun-protected skin(P＞0.05).The correlation between the expression intensity of epidermal p63 and age was negative in sun-exposed sites(r=-0.389,P=0.010),positive in sun-protected sites(r=0.341,P＜0.05).but non-significant in semi-exposed sites(P＞0.05).With regard to the expression of epidermal p63,no significant difference was observed among sun-exposed sites,sun-protected sites and semi-exposed sites in volunteers aged from 10 to 30 years.while in those aged from 31 to 50 years and from 51 to 79 years.sun-protected sites was significantly higher than semi-exposed sites followed by sun-exposed sites(all P＜0.05).There was a weak correlation between the expression intensity of epidermal CD44 and age(r=-0.083,P＜0.05),but no significant difierence was noted among the three kinds of sites(P＞0.05).Conclusions In stratum basale,the percentage of p63.expressing cells and the expression intensity Of CD44 negatively correlate with age,but have no correlation with ultraviolet irradiation.In individuals aged from 31 to 50 years and from 51 t0 79 vears.the expression of epidermal p63 decreases with the accumulation of sun-exposure.