Terminal Hair vs Vellus Hair
Terminal hair and vellus hair being two types of hair, knowing what is hair is useful for a better understanding of the difference between terminal hair and vellus hair. The presence of hairs is considered as unique mammalian characteristic feature. Hairs (hair fibers) are dead structures formed of keratin proteins and are located in tube-like hollows known as hair follicles. Keratin proteins embedded in an amorphous matrix to form hair fibers. There are three different types of hairs; lanugo hairs, vellus hairs, and terminal hairs. Lanugo hairs are only found on fetus and infants, and shed after or before the birth. The hairs retain during the adulthood are vellus and terminal hairs. Hairs are crucial for thermoregulation of mammals. Hairs act as an insulator during the cold environmental conditions and also protects the skin from UV light. All the hair follicles have the ability of producing either vellus or terminal hair and this ability varies with the age, genetics and hormones.
What is Terminal Hair?
Terminal hairs are long, coarser, pigmented and are found on the legs, arms, and scalp of both males and females. At puberty, terminal hairs start to grow on groin area and maxillae of both males and females, and also on the face of men. Unlike other types of hair, terminal hair has medulla and can be easily distinguished due to its dark color. Depending on the location and the function, the size and shape of the terminal hair varies. Terminal hairs found on the scalp are capable of providing protection against UV light while the terminal hairs found on eyebrows and eyelashes prevent the entering of dust and fluids into eyes. Furthermore, nasal hair prevents insects and other airborne materials from entering the nasal cavity.
What is Vellus Hair?
Vellus hairs are soft, fine, non-modulated, and poorly pigmented and cover the whole body except palms, soles, lips and genital areas. Females have more vellus hair than males. Vellus hairs are very common on infants and children. At puberty, most of the vellus hairs are replaced by terminal hairs.
What is the difference between Terminal Hair and Vellus Hair?
• Vellus hairs are soft fine hairs and are poorly pigmented, whereas terminal hairs are coarser and well-pigmented.
• Terminal hairs are longer than vellus hairs.
• The diameter of the terminal hair is usually more than 60 μm, whereas that of vellus hair is less than 30 µm.
• Vellus hairs are found on most areas except palms, soles, lips and genital areas, whereas terminal hairs are found on the scalp, under the arms, in the pubic region and certain other parts on skin.
• Terminal hair follicles are found deep in the dermis and their bulbs penetrated the subcutaneous fat layer. Unlike terminal hairs, vellus hair follicles penetrate up to reticular dermis and do not reach subcutaneous fat layer.
• Terminal hair has a medulla, whereas vellus hair does not.
• In certain areas, vellus hairs are replaced with terminal hairs as a result of hormonal changes occurring at the puberty.