Instruct: Given a question, retrieve relevant documents that answer the question.
Query: What is the growth rate for human hair?
The three stages of hair growth are the anagen, catagen, and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The rate or speed of hair growth is about 1.25centimetres or 0.5inches per month, or about 15 centimetres or 6inches per year.
Human population planning is the practice of intentionally controlling the rate of growth of a human population. Historically, human population planning has been implemented with the goal of increasing the rate of human population growth. However, in the period from the 1950s to the 1980s, concerns about global population growth and its effects on poverty, environmental degradation and political stability led to efforts to reduce human population growth rates. More recently, some countries, such as Iran and Spain, have begun efforts to increase their birth rates once again.
The Bolognese often appears on lists of dogs that allegedly do not shed (moult). It is true that these dogs do not seasonally moult or lose large amounts of fur as many other breeds do. However, they do eventually lose and replace individual hairs, similar to human hair growth cycles. Each hair grows from a hair follicle, which has a three phase cycle, as do most mammals. These cycles are: "anagen", growth of normal hair; "catagen" growth slows, and hair shaft thins; "telegen", hair growth stops, follicle rests, and old hair fall off—is shed. At the end of the telegen phase, the follicle begins the cycle again. The length of time of the growing and shedding cycle varies by age and other factors. There is no such thing as a completely non-shedding breed.
Blocking FGF5 in the human scalp extends the hair cycle, resulting in less hair fall, faster hair growth rate and increased hair growth., "In vitro" methods using engineered cell lines and FGFR1 expressing dermal papilla cells have identified a number of naturally derived botanical isolates including "Sanguisorba officnalis" and single molecule members of the monoterpenoid as inhibitors (blockers) of FGF5. Clinical studies have shown that topical application of formulations containing these natural extracts and molecules are beneficial in men and women experiencing hair loss.,
Growth of spermatogenic tissue in testicles, male fertility, penis or clitoris enlargement, increased libido and frequency of erection or clitoral engorgement. Growth of jaw, brow, chin, nose, and remodeling of facial bone contours, in conjunction with human growth hormone. Completion of bone maturation and termination of growth. This occurs indirectly via estradiol metabolites and hence more gradually in men than women. Increased muscle strength and mass, shoulders become broader and rib cage expands, deepening of voice, growth of the Adam's apple. Enlargement of sebaceous glands. This might cause acne, subcutaneous fat in face decreases. Pubic hair extends to thighs and up toward umbilicus, development of facial hair (sideburns, beard, moustache), loss of scalp hair (androgenetic alopecia), increase in chest hair, periareolar hair, perianal hair, leg hair, armpit hair.
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 hair. At puberty, androgen hormones cause much of the vellus hair to turn into terminal hair and stimulate 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.
The hair of the Tibetan Terrier has a long growth cycle. As a result, their coat grows quite long and pet animals will require occasional trimming. They do not shed like dogs with shorter hair growth cycles, but rather slough hair at a rate similar to that of most humans. The exception is at approximately nine months when puppies slough their entire coat in advance of acquiring their adult coat. The double coat is profuse, with a warm undercoat and a topcoat which has the texture of human hair. It should not be silky or curled, but wavy is acceptable. Long and thick, it is shown natural, but should not be so long as to touch the floor, as is typical in breeds such as the Lhasa Apso or Maltese. A fall of hair covers the face and eyes, but long eyelashes generally prevent hair from getting in the Tibetan Terrier's eyes, and the breed has very good eyesight.
The body has different types of hair, including vellus hair and androgenic hair, each with its own type of cellular construction. This varied construction gives the hair unique characteristics, serving specific purposes, mainly warmth (redundant in modern humans) and physical protection.[2] Most humans develop the longest thickest hair on their scalps and (mostly observed in males) faces. This hair will usually grow to several feet before terminating, but many humans develop much longer hair.
Traction alopecia is caused by adding too much strain on the hair on one's head. Tight ponytails and other styles that require added tension to the hair are often what cause this disease. It can also occur on the face in areas where the hair is often styled. Plucking or waxing one's eyebrows frequently, for example, can yield suppressed hair growth in the area.
When the body is under strain, it reprioritizes its processes. For example, the vital organs will be attended to first, meaning that healthy, oxygenated blood may not feed into the hair follicle, resulting in less healthy hair or a decline in growth rate. While not all hair growth issues stem from malnutrition, it is a valuable symptom in diagnosis.
The anagen phase is known as the growth phase. This is the phase where the hair physically grows approximately 1cm per month.[3] It begins in the papilla and can last from two to six years.[4][5] The span at which the hair remains in this stage of growth is determined by genetics. The longer the hair stays in the anagen phase, the longer it will grow. During this phase, cells neighboring the papilla in a germinative layer divide to produce new hair fibers,[6] and the follicle buries itself into the dermal layer of the skin to nourish the strand. About 85% - 90% of the hairs on one's head are in the anagen phase at any given time.
UV levels of either 20 or 50 mJ cm−2 in the UV-B range have been shown to inhibit hair growth, reduce hair melanin and damage hair follicles.[8]
Another mechanism involves a change in the hair cycle. There are three stages of the hair cycle: the anagen phase (hair growth), the catagen phase (hair follicle death), and the telogen phase (hair shedding). If the anagen phase increases beyond what is normal, that region of the body will experience excessive hair growth.
Most chemotherapy drugs work by attacking rapidly dividing cells. Rapid cell replication is one of the hallmarks of cancer; however, hair follicle cells also grow and divide quickly. Consequently, the chemotherapy drugs usually inhibit hair growth. The dose and type of medicine will determine the severity of hair loss. Once the course of chemotherapy has ended, new hair growth may begin after three to 10 weeks.
Different ethnic groups have observable differences in the structure, density, and growth rate of hair. With regard to structure, all human hair has the same basic chemical composition in terms of keratin protein content. Franbourg "et al." have found that Black hair may differ in the distribution of lipids throughout the hair shaft. Classical afro-textured hair has been found to be not as densely concentrated on the scalp as other follical types. Specifically, the average density of afro-textured hair was found to be approximately 190 hairs per square centimeter. This was significantly lower than that of Caucasian hair, which, on average, has approximately 227 hairs per square centimeter.
There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include "alopecia" or hair loss, "hirsutism" or excess hair growth and "lupus erythematosus".
Human hair follicles are very sensitive to the effects of radiation therapy administered to the head, most commonly used to treat cancerous growths within the brain. Hair shedding may start as soon as two weeks after the first dose of radiation and will continue for a couple of weeks. Hair follicles typically enter the resting telogen phase and regrowth should commence 2.5 to 3 months after the hair begins to shed. Regrowth may be sparser after treatment.
The protein called profis makes up hair and stimulates hair growth.
Abdominal hair is the hair that grows on the abdomen of humans and non-human mammals, in the region between the pubic area and the thorax (chest). The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax downwards to the navel. The abdominal hair of non-human mammals is part of the pelage, (hair or fur).
Seasonal changes are also known to affect hair growth. For instance, one experiment had concluded that the rate of hair growth for men and their beards was lowest in January and February and increased from March to July.
A recent development in forensic science is the isotopic analysis of hair strands. Hair has a recognisable growth rate of 9-11mm per month or 15 cm per year. Human hair growth is primarily a function of diet, especially drinking water intake. The stable isotopic ratios of drinking water are a function of location, and the geology that the water percolates through. Sr, Sr and oxygen isotope variations are different all over the world. These differences in isotopic ratio are then biologically 'set' in our hair as it grows and it has therefore become possible to identify recent geographic histories by the analysis of hair strands. For example, it could be possible to identify whether a terrorist suspect had recently been to a particular location from hair analysis. This hair analysis is a non-invasive method which is becoming very popular in cases that DNA or other traditional means are bringing no answers.
Scalp hair grows, on average, at a rate of about 1.25 centimeters per month, and shampoos or vitamins have not been shown to noticeably change this rate. Hair growth rate also depends upon what phase in the cycle of hair growth one is actually in; there are three phases. The speed of hair growth varies based upon genetics, gender, age, hormones, and may be reduced by nutrient deficiency (i.e., anorexia, anemia, zinc deficiency) and hormonal fluctuations (i.e., menopause, polycystic ovaries, thyroid disease).
The maximum terminal hair length depends on the length of the anagen (period of hair growth) for the individual. Waist-length hair or longer is only possible to reach for people with long anagen. The anagen lasts between 2 and 7 years, for some individuals even longer, and is followed by shorter catagen (transition) and telogen (resting) periods. At any given time, about 85% of hair strands are in anagen. The fibroblast growth factor 5 (FGF5) gene affects the hair cycle in mammals including humans; blocking FGF5 in the human scalp (by applying a herbal extract that blocked FGF5) extends the hair cycle, resulting in less hair fall and increased hair growth.
Exponential growth describes unregulated reproduction. It is very unusual to see this in nature. In the last 100 years, human population growth has appeared to be exponential. In the long run, however, it is not likely. Thomas Malthus believed that human population growth would lead to overpopulation and starvation due to scarcity of resources. They believed that human population would grow at rate in which they exceed the ability at which humans can find food. In the future, humans would be unable to feed large populations. The biological assumptions of exponential growth is that the per capita growth rate is constant. Growth is not limited by resource scarcity or predation.
In most people, scalp hair growth will halt due to follicle devitalization after reaching a length of generally two or three feet. Exceptions to this rule can be observed in individuals with hair development abnormalities, which may cause an unusual length of hair growth.