Human hair is a complex structure that protects the skin from external insults. It consists of three layers: the cortex, medulla, and cuticle. The cuticle consists of flat scale-like cells that slope outward from the hair follicle’s attachment point. These cells interlock with cells within the inner root sheath. Human hair has a non-repeating pattern, while animal hair has a regular repeating pattern.
Hair grows from follicles deep within the dermis. It can be found on most parts of the body, although it is most commonly noticeable in certain areas. Hair is a biomaterial that is composed of alpha-keratin. Hair can be coarse or thin, or it can be fine and vellus.
The type of hair a person has can influence their social status. Historically, hair has also been used to identify group members. For example, followers of Oliver Cromwell cut their hair close to their head, resulting in the nickname of Roundheads. Isotopic analysis of hair samples from the 19th century can shed light on how group members interacted. In the 20th century, hairstyles became increasingly popular, with bobbed hair becoming popular among flappers and female art students.
The hair follicle is connected to a tiny muscle called the arrector pili. This muscle enables blood flow to the hair bulb, providing essential elements necessary for healthy hair. Sebaceous glands are located within the follicle. They secrete sebum, which acts as a natural lubricant. The bulb of the hair also contains sweat glands.
Hair is an intricate structure, consisting of three layers. The innermost layer is made of amino acids, sugar, glycogen, and citrulline. It also contains keratin bonds and melanocytes, which produce melanin pigment. The outer layer is called the cuticle. Hair grows less than half a millimeter a day. It is always in three different stages: anagen, catagen, and telogen.
In a criminal case, the presence of hair evidence is a key factor in convicting the accused. It is easy to collect hair samples from a suspect. In fact, hair evidence is one of the most common types of evidence in criminal investigations. A forensic scientist named Edmond Locard first articulated the principles that support the concept. Locard’s Locard Exchange Principle states that any material that comes into contact with another surface will exchange a certain amount of material.
The growth phase of hair lasts between three and seven years. During the transitional phase, hair growth slows down and shrinks. The hair then goes through a resting phase, called the telogen phase, lasting about two to three months. The telogen stage is crucial for the healthy growth of hair.