Hair Follicle

Anatomy of the Hair Follicle

The Hair Follicle is a complex structure consisting of several concentric compartments that work together to produce and protect the hair shaft:

• Dermal Papilla — a vascular and connective tissue core at the base of the follicle. It contains the capillaries that supply oxygen and nutrients to the cells involved in hair production. It regulates the size of the follicle and the duration of the growth phase through the secretion of growth factors.
• Follicular Matrix — an area of intense cell proliferation immediately above the papilla. The matrix cells divide rapidly, differentiating into keratinocytes that will form the hair shaft and the root sheaths.
• Inner Radicular Sheath (IRS) — a keratinized layer that envelops the developing hair shaft and guides its outward growth.
• External Root Sheath (ERS) — the outer layer that contains the niche of follicular stem cells in the bulge region. These stem cells are essential for follicle regeneration during each cycle.
• Sebaceous Gland — a structure attached to the follicle that secretes sebum, a natural lubricant for the hair shaft and scalp.

The Hair cycle

Each Hair Follicle independently goes through a biological cycle consisting of three main phases plus a transitional phase:

• Anagen (active growth phase) — lasts 2 to 7 years on the scalp. The matrix cells actively divide, producing the hair shaft, which grows at an average rate of about 1 cm per month. Under normal conditions, approximately 85–90% of the follicles on the scalp are in the Anagen phase.
• Catagen (transition phase) — lasts 2–3 weeks. Cell division stops, the papilla retracts, and the follicle shortens. About 1–2% of follicles are in this phase at any given time.
• Telogen (resting phase) — lasts 3–4 months. The follicle is quiescent. The hair shaft transforms into a “club-shaped” hair ready to be shed. Under normal conditions, approximately 10–15% of follicles are in the Telogen phase.
• Exogen — the active shedding phase of Telogen hair, distinct from the resting phase of Telogen. The normal daily hair loss is 50–100 hairs.

A prolongation of the telogen phase or an abnormal shortening of the anagen phase leads to telogen effluvium — the most common form of hair loss, often associated with nutritional deficiencies, stress, hormonal changes, or fever.

Nutrition and the Hair Follicle

The cells of the follicular matrix are among the most metabolically active in the body: their high rate of division makes them particularly sensitive to nutritional deficiencies. The micronutrients with the most well-documented role in follicular health are:

• Biotin — an essential coenzyme for the metabolism of amino acids and fatty acids involved in keratinization. Biotin deficiencies manifest as hair shaft fragility and hair loss.
• Zinc (and Zinc Gluconate) — a cofactor for enzymes that regulate keratinocyte proliferation and Keratin synthesis. It also modulates the activity of 5-alpha reductase, an enzyme involved in androgenetic alopecia.
• Iron — Iron deficiency (even in the absence of overt anemia) is one of the most common causes of Telogen effluvium in women of childbearing age. Iron is essential for the proliferative activity of matrix cells.
• Vitamin D — Vitamin D receptors are expressed in the stem cells of the follicular bulge. Insufficient levels are associated with alterations in the hair cycle and forms of alopecia.
• Sulfur-containing Amino Acids (Cystine, Methionine) — direct precursors of Keratin. An adequate protein intake, rich in sulfur-containing amino acids, is a necessary condition for normal keratinization.
• Selenomethionine — protects follicular cells from Oxidative Stress and supports the synthesis of endogenous Antioxidant Enzymes in the hair bulb.

Hair loss can have multiple causes—hormonal, genetic, autoimmune, drug-related, or nutritional—that require a differential diagnosis by a dermatologist or a physician specializing in trichology. Nutritional supplementation can be a helpful adjunct, but it does not replace a clinical evaluation of the underlying cause.

Always remember that it is important to consult a healthcare professional before starting any new supplement or treatment.