Examination of Normal and Diseased Skin

Comaish (1968) has applied the technique of multiple internal reflection (MIR) to intact human skin in vivo. Using a germanium reflector plate he obtained spectra (in a Wilks Skin Analyzer ) of normal skin (Fig. 18.7) and various dermatoses (e.g., Fig. 18.8) and found gross changes from the normal in the lesions of psoriasis, eczema, and other disorders. He has also demonstrated abnormalities in the clinically normal skin of psoriatic patients. The technique measures surface changes, so that only the outer layers of stratum corneum, sweat, sebum, and extraneous materials will affect the results obtained. Lactic acid, lactate, and ammonia from sweat probably contribute substantially to the bands at 2935, 1465, 1125, and 1045 cm . After the skin was washed and dried these bands were diminished or disappeared entirely. Any contributions the stratum corneum makes to the infrared spectrum are at 2870, 1650, and 1550 cm .  

In the lesions of psoriasis (Fig. 18.8) the bands at 1650, 1550, 1125, 1045, and 1025 cm were grossly diminished and those at 2940, 2870, and 1465cm diminished only slightly. Also, the water bands at 3400 and 1640 cm were considerably diminished (from impaired sweating in the lesion). The band at 3400 cm was replaced 

The apparently normal palms of 10 psoriatic patients were studied. As Table 18.1 shows, the findings were significantly different from those in the palmar skin of non-psoriatic controls as measured by the height of bands recorded by a Hilger and Watts Infrascan spectrophotometer. (A Perkin-Elmer Model 157 instrument did not yield statistically significant differences, although the trend of results was similar.) 

Comaish states that it is entirely possible that certain diseases may be associated with the deposition of certain chemical compounds in amounts capable of exerting a characteristic effect on the MIR spectrum. Further observation is needed. 

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