The color of human hair

Abstract

The color of human hair is determined by melanin. Melanin is produced and packaged into membrane-enclosed melanosomes by melanocytes. The melanosomes are then embedded in a matrix of keratin-associated proteins in keratinocytes while these keratinize during hair growth. This results in a relatively uniform coloration of the entire hair shaft. Ultimately, hair color is a result of the mixing ratio of the two types of occurring melanin: The blackish-brown eumelanin and the yellowish-red pheomelanin. The genetics of hair color is still being researched. The melanocortin-1-receptor (MC1R) gene is an important component here because it plays a central role in regulating which type of melanin is produced. When the MC1R gene suffers a loss- of- function mutation, only pheomelanin is produced; this results in a red-headed, hard-to-tan phenotype. The production of both types of melanin is controlled by the rate-limiting enzyme tryosinase. Tyrosinase activity is much higher in people with red or blond hair than in people with brown or black hair. In people with grey hair, tyrosinase activity is significantly reduced as a result of aging processes. Grey hair color is a product of residual melanin pigments in the hair shaft and the intrinsic color of keratin. A person's perceived hair color is the overall impression created by the totality of colors of individual (head) hairs, which can differ in color from hair to hair. A distinction is therefore made between the macroscopic determination of hair color from a whole head of hair, or strand of hair, and the microscopic determination of color from single hairs. In both cases, the classification of hair color can be made either by subjectively comparing the hair to color scales or by using colorimetric methods. Increasingly, artificially colored hair is sent in for examination. Artificial coloring can be recognized under the microscope. The shape and color of human body hair can be different from head hair and can also display considerable intra-individual variety. It is thus not possible to conclude the color of head hair from the color of pubic hair, for example, or vice versa. Every day, a person loses about 100 telogenic head hairs. It is thus not surprising that hair is the most common material evidence found at crime scenes, and identification methods that can associate evidential hair with the person it originated from rank highly in the forensic sciences. There are both morphological and molecular genetic methods available to individualize and associate hair with potential suspects. Determining hair color is an important aspect of the morphological examination.