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The miraculous growth process of hair: what happens from root to tip?
Hair growth is a complex and wonderful process that involves the interaction of many cells from the hair follicle to the tip of the hair. Hair follicles exist in the skin of mammals, located in the dermis of the skin, and are composed of up to 20 different types of cells, each with special functions. These cells regulate hair growth through a complex interaction of hormones, neuropeptides and immune cells.
This process enables the follicles to produce different types of hair in different parts of the body, for example, terminal hair on the scalp and lanugo, the hair seen in the womb and on some newborns.
The hair growth process is divided into several stages: the growth phase (anagen), the degradation phase (catagen), the resting phase (telogen), the shedding phase (exogen), and the interval period (kenogen) between hair follicles and new hair growth. Human hair growth cycles are longer than those of other mammals, resulting in a unique hair aesthetic that reflects social and cultural norms.
The structure of the hair follicle
The distribution of hair follicles varies throughout the human body. For example, the skin on the palms and soles of the feet has no hair follicles, while the skin on the scalp, forearms, legs, and genitals has an abundance of hair follicles. The hair follicle is composed of three main structures, namely the hair follicle, sebaceous gland, and sinus muscle.
At the base of the hair follicle is a structure called the dermal papilla, which is mainly composed of connective tissue and capillary rings, and cell division here is very rare.
Hair growth and shape are influenced by genetic genes, and there are significant differences in hair characteristics between different ethnic groups. These differences include the shape, size, and location of the hair follicles.
Different stages of growth
The hair growth cycle consists of the growth phase, the regression phase and the resting phase. The growth phase is the active growth stage, during which the hair roots grow approximately 1 cm every 28 days. The length of each person's growth phase varies, ranging from two to seven years. As for the signals that hair follicles enter the regression phase, it is still unclear.
The catagen phase is a transitional phase of growth that lasts about two to three weeks, during which the hair gradually transforms into "finishing hairs," followed by the telogen phase, a resting phase that lasts about three months.
During the resting phase, when the human body is under extreme stress, up to 70% of the hair may enter this phase prematurely and fall out. This condition is called "telogen effluvium."
Clinical significance of hair follicles
Abnormal hair appearance, texture, or growth is often an early sign of a local follicle disorder or a systemic disease. Common hair follicle disorders include alopecia, overgrowth disorders, and lupus. Understanding the function of normal hair follicles is crucial for the diagnosis and treatment of many dermatological and systemic diseases.
The role of the microbiome in the biology, immunology and diseases of scalp hair follicles is also gaining increasing attention, with studies showing that changes in the scalp microbiome are associated with a variety of diseases, such as seborrheic dermatitis and alopecia.
Hair Transplantation and Restoration
There are two main methods of hair transplantation techniques: follicular unit transplantation (FUT) and follicular unit extraction (FUE). In these methods, naturally occurring follicular units are extracted from the recipient's hair follicles and then transplanted according to the patient's needs.
These follicles, which resist the effects of hormones, are still able to continue growing in their normal growth cycle, providing permanent, natural growth of hair. Although hair transplantation dates back to the 1950s, it was not until 1995 that the introduction of follicular unit transplantation technology really entered the medical literature.
With a deeper understanding of the hair growth process, we can't help but wonder whether we can better deal with hair-related health issues and explore more secrets of hair in the future?
