488 1{ \I)I A'lloN lilOLoOY 



I 



(juartz elicited siiiil)uiii. wliereas those passing through window glass did 

 ii(»t. Tills would indicate that the sunburn-inducing radiation includes 

 no wave lengths longer than those cut off by window glass, i.e., about 

 0.32 M, where modern studies show the long-wave-length limit for sunburn 

 to be.^ W'idmark was particularly concerned with sunburn of the eyes, 

 which he showed to be brought about by the same wave lengths as sun- 

 burn of the skin. By the turn of the century ultraviolet radiation .seems 

 to have been generally recognized as the cause of sunl)urn (e.g., Hammer, 

 1891; Finsen, 1900; Miiller, 1900), although the spectral region was not 

 delimited more exactly. The first attempt to do this was made by Henri 

 and Moycho in 1914 who used the rabbit as the experimental animal; but 

 the first accurate determinations on human skin were not carried out until 

 the 1920's (Hausser and Vahle, 1922; Haus.ser, 1928). 



Modern studies of sunburn date from about the same time, but, with 

 certain notable exceptions, these have been sporadic in occurrence and 

 inconclusive in character. Perhaps this may be attributed to the com- 

 plexity of the problem and the difficulties of experimentation in this field, 

 as well as to lack of interest among scientific investigators. In contrast 

 to the relative paucity of experiments on sunburn is the plethora of pop- 

 ular fancies, from which scientists are not altogether immune. A good 

 many false ideas find their explanations in unrecognized physical factors— 

 the optics of the skin or the spectral quality of sunlight; others, in the 

 complex nature of the physiological responses. It is hoped that some 

 misunderstandings may be corrected in the course of this chapter, 

 although a host of questions about sunburn will remain unanswered. 



Sunburn involves a number of tissues of the skin, and can be understood 

 only in terms of the anatomy and physiology of that organ. Frequent 

 reference is made in the following pages to layers of the skin which the 

 reader may identify in Fig. 13-1. The character of sunburn may vary to 

 some extent with the severity of exposure and from person to person, but 

 it alwa3\s presents the same general picture. An hour's exposure to bright 

 midday summer sunlight is usually followed by reddening of the exposed 

 area. This erythema of sunburn is the gross manifestation of dilation of 

 the minute vessels of the dermis. The erythema may be accompanied by 

 slight swelling, which becomes more pronounced if the exposure is pro- 

 longed. Blistering and desquamation may result from severe exposures, 

 and there may be some pain and itching. The erythema is normally 

 replaced after a few days by suntan, the brown color resulting from redis- 

 tribution and increase in the melanin pigment of the epidermis. The sun- 

 tan may persist for months or years. Not grossly observable, but of 



* Bowles (1889), who was unaware of Widmark's experiments, arrived at the con- 

 chision that ultraviolot radiation is responsible for sunburn on the basis of experiences 

 in the .\lps. The article is of interest as reflecting the generally vague ideas about 

 radiation current at that time. 



