The growth of human hair is an extremely complex process and hair loss is based on a number of factors including genetics, hormonal influence, environment issues, and health condition. Infections iron or Vitamin D deficiency, autoimmune disorders and metabolic problems can also have a role in hair loss. Nutrition also plays an important role in whether or not the body is able to produce healthy hair. Male pattern baldness affecting 35 million American men, also known as androgenetic alopecia (AGA), is X- linked and therefore largely linked to maternal genetic influence. Twenty to thirty million American women also suffer from various degrees of alopecia. Hair grows at an average rate of approximately half an inch per month. The average person has 100,000 to 150,000 hairs on their scalp at any given time. One single strand of hair is comprised of multiple microscopic, components; all of which contribute to the body’s ability to grow and maintain healthy hair. The body produces three different types of hair; the hair type found on the human scalp is known as terminal hair.
Humans are constantly in a state of growing and losing our hair. The scalp sheds hair that is dead or damaged on a daily basis. Alopecia results when the hair we lose is not replaced by new growth. One of the common trends that is seen as individuals advance in age and begin to lose primary terminal hairs on the scalp area is for it to be replaced with vellus hairs, very similar to what was present when the individual was first born as an infant before the scalp filled in with permanent hair. There are three phases in the hair growth cycle.
In the anagen phase the majority of all hairs strands are actively growing. The duration of anagen is on average three to four years but can in some cases be as long as nine years. As a result of a shortened anagen phase, individuals may notice that their hair is becoming finer and thinner with less color properties. Most of our hair is in the anagen growth phase. Only a small percentage of our hair strands are in one of the two remaining phases of cyclical hair growth.
The catagen, or hair loss phase, lasts approximately three to four weeks. On any typical day, most people shed anywhere between 75-100 scalp hairs. These hairs are lost to make way for new growth hair that will soon appear. Sometimes this hair loss is associated with brushing ones hair or shampooing.
Referred to as telogen and lasting a few months, this is the phase where hair is resting or sleeping. Hairs in the resting phase are neither growing nor falling out. They are simply sleeping. This means that there is no active growth going on with that hair strand.
There are many hair restoration techniques and cosmetic hair procedures available today. Efforts are made to match hair types and hair direction to maintain optimal appearance. There has been some recent interest in hair restoration by the uncontrolled injection of Platelet rich plasma (mostly growth factors and a few stem cells). Medications are another alternative. Currently, Rogaine and Propecia are the only two medications for baldness approved by the FDA. They are more effective for maintaining hair already on the scalp than they are in re-growing hair. Medications like Propecia cannot restore the large healthy follicles in androgenic alopecia and have been reported to have many untoward side effects, some of which appear to be permanent even after discontinuing the medication. Recent research has focused on Vitamin D and the Vitamin D receptor to stimulate hair follicle growth. Over the past decade, there has been much hope and hype for a realistic treatment for baldness using stem cell technology. For years, scientists had thought that people suffering from hair loss had a depletion of hair follicles and follicle stem cells, which are necessary to grow hair. Dr. George Cotsarelis, a professor of dermatology at the University of Pennsylvania, published a study showing that bald people have the same number of follicle stem cells as those with hair. The study was published early 2011 in the Journal of Clinical Investigation. Cotsarelis and his team analyzed skin cells from the bald and non-bald parts of the scalp of people with androgenetic alopecia. By using different markers to distinguish between stem cells and hair follicle progenitor cells, they were able to count the number of each type and they found that there was the same number of follicle stem cells in the skin from bald scalps as there were in the skin from the non-bald scalps. An inability of stem cells in the scalp to develop into the type of cells that make hair follicles may be an underlying cause of male-pattern baldness. So if researchers could identify the signals that stimulate the stem cells into producing more hair follicle progenitor cells, then it would be possible to generate bigger hair follicles that could grow hair. Such studies have shown that men with male pattern baldness still have stem cells in follicle roots but these stem cells lose the ￼ ability to initiate hair regeneration. Scientists have known that these follicle stem cells need signals from within the skin to grow hair, but the source of those signals has been unclear. A recent ground breaking report from Yale (see Horsely, et. al. published in the Sept. 2, 2011 issue of Cell) appears to demonstrate the efficacy of adipose derived stem cells in activating these dormant hair follicles and growing new hair. Horsley’s team observed that when hair dies, the layer of fat in the scalp that comprises most of the skin’s thickness shrinks. When hair growth begins, the fat layer expands in a process called adipogenesis. Researchers found that a type of stem cell involved in creation of new fat cells — adipose precursor cells — was required for hair regeneration in mice. These precursor cells are the same stem cells isolated in stromal vascular fraction by the process used at the select affiliates within the Cell Surgical Network. The Yale investigators also found these cells produce signal molecules called PDGF (platelet derived growth factor), which are necessary to produce hair growth in the mice. It still remains to be shown that PDGF has the same chemical signal effect on human hair growth. We do know that PDGF is a powerful activator of human adult mesenchymal stem cells.
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