SUNBURN 



489 



major importance with regard to sensitivity to subsequent exposure, is the 

 hyperplasia of the epidermis which results in thickening of both the horny 

 layer (corneum) and the viable malpighian layer. The hyperplasia is pre- 

 ceded by degenerative changes in epidermal cells, and there is migration 

 of leukocytes out of the vessels of the dermis. Considering these changes, 

 sunburn may be classified as an acute inflammatory process, comparable 

 to that associated with superficial burns of any kind. The term "sun- 

 burn " is used here to include all these changes without regard to the inten- 

 sity of the response, whether there is only a fleeting redness or whether 

 severe blisters develop. The term is applied when the sunburn results 



EPIDERMIS 



DERMIS 



OR -^ 

 CORlUM 



Fig. 13-1. Diagram of cross section of skin from the human shoulder, showing the 

 various layers to which reference will be made in the text. The epiderrnis is the outer 

 layer consisting of: sc, the stratum corneum or horny layer, and sm, the stratum Mal- 

 pighii. The cells at the bottom of the malpighian layer constitute the basal cell 

 layer b. The "prickle" cells lie superficial to the basal cells. The dermis or corium 

 includes the tissues of the skin lying beneath the basal cell layer of the epidermis. In 

 the papillary layer of the corium are situated the most superficial blood vessels (v). 

 (After Maximov and Bloom, 1940.) 



from exposure to ultraviolet radiation from an artificial source as well as 

 when it is caused by natural sunlight. 



Various aspects of sunburn stem from the action of ultraviolet radiation 

 of wave lengths shorter than about 0.32 p on the cells of the malpighian 

 layer of the epidermis. The effects on the cells are no doubt comparable 

 to those of ultraviolet radiation on living cells in general, but they are 

 manifested here in terms of a complex of secondary processes.'^ These 

 may be treated separately for purposes of study so long as their basic 

 origin and interrelations are not lost sight of. In this chapter various 

 responses which follow the primary photochemical reaction in the cells of 

 the malpighian layer will be considered separately. Later, the mechanism 

 as a whole and the factors influencing sunburn under conditions of natural 

 sunlight will be considered. Sunburn of the eyes also occurs and may be 



' That ultraviolet radiation may have more than one primary effect on the cell is 

 shown bv Blum et nl. (1954). 



