How does hair grow

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Last updated: April 8, 2026

Quick Answer: Hair grows from follicles in the skin through a cycle with three phases: anagen (growth), catagen (transition), and telogen (resting). Scalp hair typically grows about 0.3-0.4 mm per day, or 6 inches (15 cm) per year, with the anagen phase lasting 2-7 years. This process is regulated by hormones, genetics, and nutrients like proteins and vitamins, with hair loss conditions like androgenetic alopecia affecting up to 50% of men by age 50.

Key Facts

Hair grows from follicles in the skin, with about 5 million follicles on the human body and 100,000-150,000 on the scalp.
The hair growth cycle consists of three phases: anagen (growth, 2-7 years), catagen (transition, 2-3 weeks), and telogen (resting, 3-4 months).
Scalp hair grows at an average rate of 0.3-0.4 mm per day, or about 6 inches (15 cm) per year.
Hair growth is influenced by genetics, hormones (e.g., androgens), age, and nutrients like proteins, vitamins (e.g., biotin), and minerals (e.g., iron).
Common hair loss conditions include androgenetic alopecia, affecting up to 50% of men by age 50 and 40% of women by age 70.

Overview

Hair growth is a complex biological process that has fascinated humans for millennia, with evidence of hair care practices dating back to ancient civilizations like Egypt around 3000 BCE. Hair serves multiple functions, including thermal insulation, sensory perception, and social signaling, with cultural significance varying across societies—for example, in many cultures, long hair symbolizes health or status. The scientific study of hair, or trichology, emerged in the 19th century, with key discoveries like the hair growth cycle by researchers in the early 1900s. Today, understanding hair growth is crucial for addressing conditions like alopecia, which affects millions globally, and for advancements in cosmetics and medical treatments. The global hair care market was valued at over $90 billion in 2023, reflecting its economic and social importance.

How It Works

Hair growth occurs in hair follicles, tiny structures in the skin's dermis layer, through a regulated cycle. The process begins in the anagen phase, where follicle cells rapidly divide, pushing the hair shaft upward at about 0.3-0.4 mm daily; this phase lasts 2-7 years for scalp hair but shorter for body hair. Next, the catagen phase involves follicle shrinkage over 2-3 weeks, detaching the hair from its blood supply. Finally, the telogen phase is a resting period of 3-4 months, after which the hair sheds naturally, and the cycle restarts. Growth is driven by stem cells in the follicle bulge and influenced by factors like genetics, hormones (e.g., androgens stimulate facial hair), and nutrients—proteins like keratin are essential for hair structure. Disruptions, such as hormonal imbalances or nutrient deficiencies, can lead to conditions like telogen effluvium, where excessive shedding occurs.

Why It Matters

Understanding hair growth has significant real-world impacts, from medical treatments to personal well-being. In healthcare, insights into hair cycles help diagnose and treat conditions like alopecia, with therapies such as minoxidil (approved by the FDA in 1988) promoting growth by extending the anagen phase. This knowledge also aids in managing chemotherapy-induced hair loss, improving patient quality of life. In cosmetics, it drives innovations in shampoos, conditioners, and supplements targeting hair health, contributing to a multi-billion-dollar industry. Socially, hair affects self-esteem and identity, with hair loss often linked to psychological distress; thus, advancements in hair restoration, like follicular unit transplantation, offer practical solutions. Overall, hair growth research enhances both clinical outcomes and daily life, highlighting its broad relevance.