The forensic examination of hairs

Hairs are an extremely common, if not ubiquitous, biological material typically recovered when searching items or scenes encountered in forensic investigations. The reason for this is simple – animals (including humans) lose or shed their hairs. In non-human animals hair loss is most often seasonal or cyclical and animals are said to moult. In humans, hair loss is random because the growth cycle of the follicles, from which hairs grow, are not synchronised. It has been estimated that humans lose in the order of 100–150 scalp hairs each day. A visual inspection of a bathroom floor or a bed sheet will readily confirm that hair loss is also not restricted to the scalp. Any owner of a cat or dog can also attest to the fact that animal hairs are shed in large numbers and can be difficult to remove. Furthermore, there is almost no limitation in the types of forensic investigation where hairs may be found and have the potential to provide useful information.