International Journal of Trichology

LETTER TO EDITOR
Year
: 2011  |  Volume : 3  |  Issue : 2  |  Page : 128--129

Optical detection of hairs


Rajiv Saini 
 Departments of Periodontology and Oral Implantology, Rural Dental College, Loni, Maharashtra, India

Correspondence Address:
Rajiv Saini
Departments of Periodontology and Oral Implantology, Rural Dental College, Loni, Rahata, Ahmednagar, Maharashtra - 413 736
India




How to cite this article:
Saini R. Optical detection of hairs.Int J Trichol 2011;3:128-129


How to cite this URL:
Saini R. Optical detection of hairs. Int J Trichol [serial online] 2011 [cited 2019 Dec 13 ];3:128-129
Available from: http://www.ijtrichology.com/text.asp?2011/3/2/128/90849


Full Text

Sir,

The optical properties of an individual hair strand are mainly determined by the translucent material of the hair, the amount of pigmentation the hair contains, and the geometric properties of the surface of the hair strand. A hair fiber is a translucent material with a regular refractive index of 1.55. The cortex of the hair fiber contains grains of melanin, which are responsible for the coloring of the hair. There exist two types of melanin: the most common type is eumelanin, which is responsible for the black or brown coloring of the hair, and there is the less common pheomelanin, which colors the hair yellow or red. As with human skin, the color of hair is determined by the melanin content. The darker eumelanin and the lighter pheomelanin are distributed in different proportions in human hair, which result in the different color tones of hair among different people. In science, a grouping of 11 to 12 different color tones are used, ranging from black to light blond. The natural appearance of a person's hair is genetically determined and depends on the skin tone and the eye color of that person. In gray hair, the hair shaft does not store pigment; the production of melanin has subsided and the melanin is replaced with deposited air bubbles.

The special structure of the surface of the hair, composed of overlapping scales, has a major influence on how the hair interacts with light. As a semi-transparent cylinder, a portion of the light is reflected directly off the fiber surface, which causes a specific reflection with the same color as the incident light. Another portion of the light penetrates the fiber by refraction, is absorbed partially, and then returns through subsurface scattering to the outside, causing a diffuse reflection with the same color as the pigments within the fiber. But unlike a perfect cylinder, the surface of the fiber has scales, which diverge the light rays slightly by an amount of just about 3°. This divergence causes the phenomenon of dispersion. Because of the scales, specular reflection and internal reflection follow different directions and produce separate peaks of reflection. The specular reflection is the primary hair reflection and has the same color as the light, the internal reflection is the secondary hair reflection and adapts to the color of the pigments present within the hair.

The high resolution offered by scanning electron microscopy (SEM) makes this technique ideal for observing morphological changes induced by chemical agents on the hair fiber. Similarly, optical microscopy tools, though having lower spatial resolution relative to SEM, are useful for inspecting the morphology of both the surface and the interior of hair. [1],[2]

References

1Lagarde JM, Peyre P, Redoules D, Black D, Briot M, Gall Y. Confocal microscopy of hair. Cell Biol Toxicol 1994;10:301-4.
2Formanek F, DE Wilde Y, Luengo GS, Querleux B. Investigation of dyed human ahir fibres using apertureless near-field scanning optical microscopy. J Microsc 2006;224:197-202.