The construction and performance of equipment consisting of a 1600 W xenon arc light source and a grating monochromator are described. Its suitability for use in the investigation of the reaction of the skin to ultraviolet (UV) radiation and to visible light is discussed.

SUMMARY.— Using an electrolytic hygrometer, the Transepidermal Water Loss (T.W.L.) from the skin was measured in normal individuals and in patients with dermatitis (eczema). It was found that there was a close correlation between T.W.L. and the state of activity of the dermatitis; and that there was a gradual reduction in abnormally raised T.W.L. in parallel with the return to normal of the skin response (dermatitis). Sweating did not contribute to the increased insensible water loss in dermatitis under the fixed limits of ambient temperature and humidity of this investigation.

SUMMARY In a Study of thirty‐four male subjects suffering from the syndrome of chronic photosensitivity dermatitis and actinic reticuloid the clinical, histological and photobiological features were such as to suggest that they were in fact examples of a single entity in which the degree of response to ultraviolet and visible light varied. Although a wide action spectrum involving UV and visible wavelengths invariably occurred with the classical clinical and histological features of actinic reticuloid (Ive et al., 1969) a broad action spectrum with similar histological appearances was also noted in some of the subjects in whom the morphological changes were those of a chronic dermatitis confined to exposed sites.

The clinical features, action spectrum and subsequent course, are described in 33 subjects with thiazide-induced photosensitivity. The reaction appeared to be phototoxic in nature. The wavelengths involved were those of the longer UVA and, not infrequently, also the shorter UVB waveband. In most instances withdrawal of the drug resulted in clearance of the clinical reaction and a return of the action spectrum to normal. In the few subjects in whom the photosensitivity persisted, either in the form of the clinical reaction or an abnormal action spectrum, or both, either a specific photodermatosis was present or another potentially photoactive drug was being taken. In no instance, was there evidence of the induction of long-term chronic photosensitivity (persistent light reaction) following the withdrawal of the thiazide drug.