Vellus
Encyclopedia
Vellus hair, colloquially called 'peach fuzz' or 'bum fluff', is short, fine, light-colored, and barely noticeable hair that develops on most of a person's body from his/her childhood
. Exceptions include the lip
s, the back of the ear
, the palm of the hand
, the sole of the foot, some external genital areas, the navel
and scar
tissue. The density of hair – the number of hair follicle
s per area
of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm (1/13 inch) long and the follicle
is not connected to a sebaceous gland
.
Vellus hair is most easily observed on children and adult women, as they generally have less terminal hair
to obscure it. Vellus hair is not lanugo
hair. Lanugo hair is a much thicker type of hair that, in human forms, normally grows only on fetuses.
Vellus hair is differentiated from the more visible terminal
or androgenic hair
, which develops only during and after puberty
, usually to a greater extent on men than it does on women.
. At puberty
, the androgen
hormone causes much of the vellus hair to turn into terminal hair
and stimulates the growth of new hair in the armpit and the pubic area
. In men, this change in vellus hair occurs on the face and the body.
There are similarities in vellus hair and intermediate hair. Neither a vellus strand nor an intermediate strand has a distinct medulla. Hormones in the body cause the hair follicle to change a strand of vellus hair into a strand of intermediate hair. This process occurs at puberty.
hormone in a person with Cushing's syndrome
. Anorexia nervosa
increases vellus hair. Vellus hair can also be found in men with male pattern baldness or hirsutism
. Hormonal fluctuations in pregnant women cause foetal vellus hair to change to terminal hair. The terminal hair is usually shed after the birth of the baby upon the return of the hormones to the normal levels.
Childhood
Childhood is the age span ranging from birth to adolescence. In developmental psychology, childhood is divided up into the developmental stages of toddlerhood , early childhood , middle childhood , and adolescence .- Age ranges of childhood :The term childhood is non-specific and can imply a...
. Exceptions include the lip
Lip
Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech...
s, the back of the ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
, the palm of the hand
Hand
A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...
, the sole of the foot, some external genital areas, the navel
Navel
The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...
and scar
Scar
Scars are areas of fibrous tissue that replace normal skin after injury. A scar results from the biological process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. With the exception of very minor lesions, every wound results in...
tissue. The density of hair – the number of hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
s per area
Area
Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...
of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm (1/13 inch) long and the follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
is not connected to a sebaceous gland
Sebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
.
Vellus hair is most easily observed on children and adult women, as they generally have less terminal hair
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
to obscure it. Vellus hair is not lanugo
Lanugo
Lanugo is fine, downy hair as a type of fur. It is often found in teratomas .-Fetal development:Lanugo grows on fetuses as a normal part of gestation, but is usually shed and replaced by vellus hair at about 33 to 36 weeks of gestational age...
hair. Lanugo hair is a much thicker type of hair that, in human forms, normally grows only on fetuses.
Vellus hair is differentiated from the more visible terminal
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
or androgenic hair
Androgenic hair
Androgenic hair, colloquially body hair, is the terminal hair that develops on the body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color. The growth of androgenic hair is related to the level of androgens in...
, which develops only during and after puberty
Puberty
Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...
, usually to a greater extent on men than it does on women.
Production
Vellus hair replaces lanugo hair on a human fetus at 36 to 40 weeks of gestation. The growth cycle of vellus hair is different from the growth cycle of terminal hairTerminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
. At puberty
Puberty
Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...
, the androgen
Androgen
Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...
hormone causes much of the vellus hair to turn into terminal hair
Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body...
and stimulates the growth of new hair in the armpit and the pubic area
Pubic hair
Pubic hair is hair in the frontal genital area, the crotch, and sometimes at the top of the inside of the legs; these areas form the pubic region....
. In men, this change in vellus hair occurs on the face and the body.
Function
Vellus hair provides both thermal insulation and cooling for the body. This insulation regulates body temperature. The function of vellus hair on sweat is that of a wick. While a skin pore is open, sweat wets a strand of vellus hair. The sweat on the external part of the strand evaporates. More sweat wets the external part of the vellus strand and then evaporates. This process is perspiration.There are similarities in vellus hair and intermediate hair. Neither a vellus strand nor an intermediate strand has a distinct medulla. Hormones in the body cause the hair follicle to change a strand of vellus hair into a strand of intermediate hair. This process occurs at puberty.
Complications
The unusual growth of vellus hair is a side effect of some types of disease and some types of mental disorder. An abundance of vellus hair can develop from an increase in the production of the cortisolCortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
hormone in a person with Cushing's syndrome
Cushing's syndrome
Cushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone or CRH...
. Anorexia nervosa
Anorexia nervosa
Anorexia nervosa is an eating disorder characterized by refusal to maintain a healthy body weight and an obsessive fear of gaining weight. Although commonly called "anorexia", that term on its own denotes any symptomatic loss of appetite and is not strictly accurate...
increases vellus hair. Vellus hair can also be found in men with male pattern baldness or hirsutism
Hirsutism
Hirsutism or frazonism is the excessive hairiness on women in those parts of the body where terminal hair does not normally occur or is minimal - for example, a beard or chest hair. It refers to a male pattern of body hair and it is therefore primarily of cosmetic and psychological concern...
. Hormonal fluctuations in pregnant women cause foetal vellus hair to change to terminal hair. The terminal hair is usually shed after the birth of the baby upon the return of the hormones to the normal levels.