ALL ABOUT HAIR: STRUCTURE AND HAIR CYCLE

Hair is made up of two distinct parts: the hair shaft, visible on the surface, and the follicle, located under the scalp. On average, a healthy scalp is home to between 100,000 and 150,000 hairs , each following a life cycle. Each hair goes through approximately 20 to 25 cycles throughout life, each cycle comprising a phase of active growth followed by a period of rest and natural shedding, explaining daily hair loss (a daily loss of 100 to 150 hairs indicates healthy hair activity, beyond this can describe abnormal shedding ). The hair fiber, composed of 95% keratin , evolves under the influence of biological and hormonal mechanisms that determine its growth, texture and density.

The hair shaft, more commonly called hair, is made up of about 95% keratin , an essential fibrous protein that ensures the strength of hair. This keratin is accompanied by about 3% water , which contributes to its flexibility, and about 2% lipids and trace elements , responsible for shine and protection against external aggressions. These components are organized into three distinct layers:

• The cuticle : Thin and transparent, it represents the outer layer of the hair shaft. Made up of flat cells superimposed like scales, the cuticle protects the fiber and influences the shine and softness of the hair.
• The cortex : The main component of the hair fiber, it contains twisted keratin fibers, responsible for the strength and elasticity of the hair. It is also in the cortex that melanin is found, a natural pigment that determines the color of the hair.
• The medulla : Located in the center of the hair, the medulla is a layer of loosely packed cells, present mainly in thick hair. Its exact role remains partially unknown, but it seems to contribute to the thermal insulation and density of the hair.

Hair growth is based on a life cycle, which repeats itself 25 to 30 times during a lifetime, influenced by genetic, hormonal, and environmental factors.

Each hair follicle follows a life cycle divided into three distinct phases, each with a specific duration and function:

• Anagen phase : The active growth phase, which lasts from 2 to 7 years depending on the individual, especially gender. Approximately 85% of the hair on the scalp is in this phase at any given time. The growth rate varies between 1 and 1.5 cm per month , depending on genetic and hormonal factors.
• Catagen phase : A brief transition phase lasting 2 to 3 weeks . During this period, growth ceases and the follicle shrinks, interrupting the hair's nourishment.
• Telogen phase : The resting phase, which lasts 2 to 4 months . At this stage, about 10 to 15% of the hair rests waiting to fall out naturally, pushed out by a new hair shaft.

• Genetics : Genes determine hair density, texture, and length of growth cycles. Some individuals have a longer anagen phase, which allows their hair to grow longer before falling out.
• Hormones : Androgenic hormones, such as testosterone , influence the duration of growth phases and can cause variations in hair density.
• Age : Over time, hair cycles shorten and follicles may become inactive, leading to decreased hair density.

• The role of the hair follicle : The hair follicle, located in the dermis, is the center of hair production. It houses the dermal papilla, a dense network of blood capillaries that provide essential nutrients and oxygen for cell division in the bulb. The health of this hair system is crucial for optimal hair growth, ensuring that the hair progresses healthily through all three phases of the cycle.

• Keratin synthesis : Keratin, a protein that makes up about 95% of the hair fiber, is produced by keratinocytes in the hair bulb. An adequate supply of amino acids, especially cysteine, is essential for its production.

• The role of scalp balance : A healthy scalp, with a balanced microbiome, indirectly participates in hair growth by maintaining a favorable environment for the follicle.

The scalp is the fundamental foundation of each hair follicle. Good hair health starts with a healthy scalp, capable of nourishing and oxygenating the follicles. Optimal blood circulation promotes hair growth and strengthens its vitality, while a balanced microbiome protects against imbalances such as hyperseborrhea , which can weaken the fibers. To help maintain an optimal balance or restore it, the Fauve Detox Serum is an ideal ally, purifying the scalp without attacking its natural microbiome.

Hair texture depends mainly on the shape of the hair follicle and the composition of the hair fiber. Here is an overview of the main hair types and their biological specificities:

• Straight Hair : Produced by round-shaped follicles, straight hair has a smoother, closed cuticle, providing better protection against external aggressions.
• Wavy hair : Their follicle is slightly oval, which gives them a natural wave. This type of hair has a good balance between volume and flexibility.
• Curly Hair : Flatter follicles produce tight curls. This hair, although voluminous, requires specific care to prevent breakage and maintain moisture.
• Kinky Hair : Kinky hair results from curved follicles. It has a high density but is more fragile due to its spiral structure, requiring nourishing and protective care.