7.1 Hair Structure & the Growth Cycle

Hair Structure & the Growth Cycle

Every hair removal service — waxing, threading, sugaring, or tweezing — works with the same underlying biology. Before you can explain to a client why one area regrows faster than another, or why a service works better at certain intervals, you need to understand what a hair actually is and how it grows. This is foundational content across every hair removal method tested under New York's Superfluous Hair curriculum unit, the single largest non-facial unit in the 19 NYCRR §162.2 esthetics curriculum at 60 hours.

Anatomy of a Hair

A single hair is made up of two connected structures: the part you can see and the part you can't.

• Hair shaft — the visible portion of the hair that extends above the surface of the skin. It is composed of keratinized (dead) protein cells and has no nerve endings, which is why cutting or trimming hair doesn't hurt.
• Hair follicle — a tube-shaped depression in the skin, extending down through the epidermis into the dermis, from which the hair grows. The follicle houses and shapes the hair root.
• Hair root — the portion of the hair that is below the surface of the skin, inside the follicle. This is the living part of the hair structure during active growth.
• Hair bulb — the thickened, rounded structure at the base of the follicle that encases the dermal papilla. The bulb is where new hair cells are produced.
• Dermal papilla — a small, cone-shaped structure at the very base of the follicle that contains the blood supply nourishing the hair. As long as the papilla is intact and healthy, the follicle can continue producing new hair.

Understanding this anatomy matters directly for hair removal: methods like waxing, threading, and tweezing pull the hair shaft and root out of the follicle, but they do not destroy the papilla or the follicle itself — which is exactly why hair grows back after these temporary methods. Only methods that damage or destroy the papilla (like electrolysis) or the follicle's ability to produce hair (like laser) can be considered permanent — and unlike most other states, New York actually keeps laser hair removal within the esthetics/cosmetology license, while electrolysis licensure should be confirmed directly with NYSDOS (both are covered in 7.3).

The Three Phases of the Hair Growth Cycle

Hair does not grow continuously and indefinitely. Each individual follicle cycles independently through three distinct phases, meaning that at any given time, the hairs on a client's leg or upper lip are all in different phases simultaneously — this is exactly why hair never seems to "all fall out" or "all show up" at once.

Because every follicle is on its own independent clock, a single hair removal session can never catch 100% of a client's hair in anagen. This is the biological reason estheticians recommend a series of regularly spaced appointments (commonly every four to six weeks for waxing) rather than a single visit: repeated services catch more and more follicles while they're in anagen, and over time this can lead to finer, sparser-looking regrowth. It also explains why a client may see some stubble reappear within days of a service — those follicles were in catagen or early anagen at the time of the appointment and were never fully dormant.

Vellus vs. Terminal Hair

Not all body hair is the same, and the exam expects you to distinguish between the two basic types:

• Vellus hair — fine, soft, short, and usually unpigmented or very lightly pigmented. Often called "peach fuzz," it covers most of the body and is barely noticeable. Vellus hair has a small, shallow bulb and is not usually connected to a sebaceous gland.
• Terminal hair — coarse, thick, longer, and typically pigmented. Terminal hair has a deep, well-developed bulb and root. It's found on the scalp, eyebrows, and lashes in everyone, and — depending on genetics and hormones — can also appear on the face, chest, back, abdomen, and limbs.

Most hair removal services target terminal hair, since it's the type clients typically want addressed. Vellus hair can also be removed cosmetically (for example, light dermaplaning or waxing of fine facial hair), but it is far less commonly the primary service goal.

What Influences Hair Growth

Several factors determine how much terminal hair a person has and where it appears:

• Genetics — ethnicity and family history strongly influence hair density, thickness, color, and distribution pattern.
• Hormones — androgens (male hormones present in both sexes to varying degrees) can trigger vellus hair to convert into coarser terminal hair, which is why hair growth patterns often shift noticeably during puberty, pregnancy, and menopause.
• Age — hair density and growth rate change across the lifespan, and hormonal shifts with age can alter both texture and location of terminal hair.

Hirsutism: A Referral, Not a Diagnosis

Hirsutism is the medical term for excessive terminal hair growth in a male-pattern distribution (face, chest, back, abdomen) on a person who wouldn't typically be expected to have hair in that pattern. When a client reports sudden or rapidly progressing excess hair growth — especially alongside other changes like irregular periods, acne, or voice changes — this can indicate an underlying hormonal condition (such as polycystic ovary syndrome) that requires medical evaluation.

The critical exam point: an esthetician is not licensed or qualified to diagnose the cause of hirsutism. Your role is limited to recognizing when a change in hair growth pattern looks abnormal or sudden and referring the client to a physician for evaluation, while continuing to provide hair removal services as requested within your scope of practice. Estheticians who attempt to diagnose or promise to "fix" a hormonal condition through hair removal services are operating outside their scope of practice.