Long-term chronic sun exposure: protecting the skin against ultraviolet radiation?
The statistically significant difference between exposed and protected skin in terms of the number of cells expressing immunological markers in the epidermal segments between the cones suggests that stimulation of the epidermis by UVR promotes hyperproliferation of cells in the cones of the basal layer, with consequent extension of the epidermal projections between the cones. This process results in a greater number of cell layers, thus acting as a defense against UVR injury.2
This finding leads us to believe in the existence of an adaptive phenomenon of protection, which occurs in response to long-term chronic exposure of the skin to UVR and is similar to that which occurs during the cicatrization of injuries to the epidermis, ie the cones move deeper within the dermis, consequently increasing the distance between the cones and the keratinocytes capable of mitosis in response to UVR. Cell migration between cones increases the number of keratinocytes that are in the post-mitotic phase and, therefore, more prone to apoptosis.2
These changes suggest that long-term sun exposure promotes tolerance to UVR, which protects against immunosuppression Our hypothesis is that chronic and long-term exposure triggers an immunologic adaptation represented by (i) elastosis protection against penetration by UVR and (ii) greater vascularization, promoting leukocyte influx. Future research must answer questions about how long the exposure must be to trigger these phenomena, whether individuals in other occupations develop this protection, and whether women have the same immunologic response.