THE CLINICAL IMPORTANCE OF WEATHERING IN HUMAN HAIR
THE CLINICAL IMPORTANCE OF WEATHERING IN HUMAN HAIR
复制标题
DOI：
10.1111/j.1365-2133.1976.tb15545.x
复制
发表时间：
1976-01-01
影响因子：
10.3
通讯作者：
ROOK A
中科院分区：
文献类型：
--
作者：
ROOK A
The term'weathering'as applied to hair is familiar to the textile scientist (Robbins, 1967) and to the cosmetic chemist (Brown & Swift, 1975), but much less so to the dermatologist. Yet weathering, a term which conveniently describes the cumulative effect of climatic exposure on the chemical and physical structure of the hair shaft, is a factor in many clinical syndromes in the dermatological department. It may be solely responsible for grossly evident abnormalities, but produces its more striking effects in combination with cosmetic procedures, or when acting on hair which is already defective. The clinical importance of weathering has been greatly increased by the recent popularity of wearing the hair long. The duration of anagen, which is probably genetically determined, ranges from 3 to 6 years, and the length of uncut hairs from 50 to 80 cm. With the scanning electron microscope (SEM) it has been shown (Bottoms, Wyatt & Comaish, 1972) that apparently normal hair shafts show a progressive loss of cuticular scale pattern from root to tip. In man it is difficult to differentiate the eflFect of weathering alone from the combined effect of weathering and trauma inflicted for cosmetic purposes, since even the more uncouth seldom refrain completely from the use of a brush and comb. Even combing adds to the erosion of cuticular scales, the margins of which are gradually chipped away to leave the cortex more or less exposed. Variation in the degree of cuticular erosion in different areas of the scalp could be related to combing habits (Swift & Brown, 1972). In a recent investigation (Brown & Swift, 1975) of hair at least 50 cm long (and therefore, at its tip, exposed to weathering for at least 3 years) it was shown that the hair near the root fractured in a strikingly different fashion from the same hair near its tip. Segments of hair were extended in a tensile tester until they fractured, and the fractured surfaces were then examined in the SEM. Near the root end the hair showed a clear transverse fracture,'as if cut with a knife'. Near the tip of extremely weathered hairs the fracture was ragged, the cortex separating into fibrillae, with longitudinal splits extending back along the shaft. In intermediate segments the type of fracture was as expected again related to the degree of weathering. Combing experiments carried out in the SEM showed that tangled hairs, forming tight bands and loops, fracture in a similar fashion.The changes produced by cold-waving solutions or by the application of excessive heat in waving or dyeing have been carefully studied, since they are often readily detectable with the light microscope (Braun, 1963). In the SEM (Orfanos & Mahrle, 1971) such insults, usually in combination with the mechanical trauma of brushing and combing, have been shown to produce fracture and detachment of free edges of cuticular cells, the pattern of which becomes disorderly. With increased or repeated injury the cuticular cells separate, exposing the cortex. Such changes obviously are more marked as the distance from the scalp increases, since such hair has had greater exposure to weathering as well as to previous cosmetic procedures, and although they necessarily resemble in general those attributed to weathering alone, extensive exposure to individual chemical or physical agents may produce different and distinctive changes (Orfanos & Mahrle, 1971).
