Trichology Basics

Trichology Glossary: 78 Hair and Scalp Terms A to Z

Trichology glossary of 78 hair and scalp terms, A to Z. Plain definitions of anagen, alopecia, cuticle, sebum, trichoscopy and more, checked against sources.

By USTI Education TeamPublished Oct 4, 202612 min read

Student drawing hair follicle and growth cycle diagrams in a notebook

Key takeaways

Trichology is the study of the hair and scalp. In the US a trichologist is a non-medical professional who recognizes, supports and refers, and does not diagnose.
The hair growth cycle has a growth phase (anagen), a transition phase (catagen) and a resting phase (telogen). Exogen is the release of the old hair.
Alopecia is the medical term for hair loss. Effluvium means excessive hair shedding, and it comes in anagen and telogen forms, according to DermNet.
Cicatricial alopecia means scarring hair loss. DermNet describes it as bald patches with no visible follicles, and the loss is typically permanent.
The hair shaft has three layers: the cuticle on the outside, the cortex that makes up most of its mass, and the medulla at the center of coarser hairs.
Hirsutism is male-pattern hair growth in women. Hypertrichosis is excessive hair growth beyond the normal for a person's age, sex and race.

This trichology glossary defines 78 hair and scalp terms in plain language, from anagen to yellow dots. Trichology is the study of the hair and scalp: how hair grows, what the fiber is made of, and what changes when something goes wrong. Each entry is one to three sentences so it can be read on its own.

New to the subject? Start with what is trichology, then come back here when a word stops you. USTI content is educational and non-medical. In the US a trichologist recognizes, supports and refers. The disease names below are here so you can describe what you see and understand a physician's notes, not so you can diagnose.

How should you use this trichology glossary?

Use it as a reference while you study or write up a consultation. The trichology terms are grouped by letter. Where USTI has a full article on a term, the entry links to it. Numbers are attributed to a named source, and every source is listed at the end.

Which trichology terms are most often confused?

Several pairs of trichology definitions sound alike but mean different things. This table sets the common pairs side by side.

Term pair	The difference
Alopecia vs effluvium	Alopecia is hair loss of any kind. Effluvium is excessive shedding.
Anagen effluvium vs telogen effluvium	Anagen effluvium has a sudden onset and affects growing hairs. Telogen effluvium appears 2 to 6 months after a trigger, according to DermNet.
Scarring vs nonscarring alopecia	In scarring (cicatricial) alopecia the follicle is destroyed. In nonscarring alopecia the follicle remains.
Vellus vs terminal hair	Vellus hair is fine and usually unpigmented. Terminal hair is thick and pigmented.
Hirsutism vs hypertrichosis	Hirsutism is male-pattern growth in women. Hypertrichosis is excess hair in any pattern.
Dandruff vs seborrheic dermatitis	DermNet describes dandruff as the uninflamed form of seborrheic dermatitis on the scalp.
Trichoscopy vs dermoscopy	Dermoscopy is magnified examination of the skin. Trichoscopy is dermoscopy of the hair and scalp.
Trichoptilosis vs trichorrhexis nodosa	Trichoptilosis is a split at the end of the hair. Trichorrhexis nodosa is a fracture point along the shaft.

A

Alopecia. The medical term for hair loss. It describes the sign, not the cause, so it is usually paired with a second word that names the type. See types of hair loss for stylists.

Alopecia areata. An autoimmune condition in which the immune system attacks hair follicles. DermNet says it typically presents with discrete bald patches on the scalp. See the alopecia areata guide for stylists.

Alopecia totalis. A form of alopecia areata with complete loss of scalp hair.

Alopecia universalis. The most extensive form of alopecia areata, with complete loss of body hair.

Anagen. The growth phase of the hair cycle. Cleveland Clinic gives its length on the scalp as 2 to 7 years. See hair growth cycle stages.

Anagen effluvium. Sudden shedding of hairs that are still in the growth phase. DermNet lists medications, especially chemotherapy, among the causes.

Androgenetic alopecia. Pattern hair loss influenced by androgens and genetics. DermNet notes it tends to affect the vertex and temples in males and the front of the scalp in females.

Arrector pili. The small muscle attached to the follicle at the bulge. When it contracts, the hair stands up and the skin forms goosebumps.

B

Black dots. A trichoscopy term for follicular openings that contain the remains of pigmented hairs broken at scalp level.

Bulb. The rounded base of the hair follicle. It holds the matrix, which surrounds the dermal papilla.

Bulge. The region of the follicle where the arrector pili muscle attaches. StatPearls notes that it contains stem cells.

C

Catagen. The short transition phase between growth and rest. Cleveland Clinic says it lasts about 2 weeks.

CCCA (central centrifugal cicatricial alopecia). A scarring hair loss that the AAD says often begins in the center of the scalp and is more commonly seen in Black women. See CCCA early signs for stylists.

Cicatricial alopecia. Scarring hair loss. Inflammation destroys the follicle, and DermNet describes the result as bald patches with no visible follicles. The loss is typically permanent.

Cortex. The middle layer of the hair shaft and most of its mass. It is built from elongated cells that hold keratin and melanin.

Cuticle. The outer layer of the hair shaft, made of flat overlapping scales. It protects the cortex and is the first layer damaged by chemical and physical wear.

D

Dandruff. Visible flaking of the scalp without redness. See dandruff vs dry scalp vs buildup.

Dermal papilla. A small structure at the base of the follicle that contains capillaries. It interacts with the matrix cells that build the hair.

Dermatologist. A medical doctor who specializes in conditions of the skin, hair and nails. Diagnosis and medical care of hair and scalp disease belong here.

Dermoscope. A handheld magnifier with a built-in light, used to examine the skin surface. Also called a dermatoscope. When used on the hair and scalp it is often called a trichoscope.

Dermoscopy. Examination of the skin using surface microscopy.

Disulfide bond. A strong chemical link between keratin chains that helps give hair its shape. Chemical straightening and waving work by breaking and re-forming these bonds.

E

Effluvium. Excessive hair shedding. See hair shedding vs hair loss.

Exclamation mark hair. A short broken hair that is thicker at the tip and thinner where it enters the scalp. DermNet describes it at the edges of alopecia areata patches.

Exogen. The part of the cycle in which the old resting hair is released from the follicle and shed.

F

Follicle. The tube-like structure in the skin that surrounds the root of a hair and produces the hair shaft.

Follicular opening. The point on the scalp surface where a follicle opens. Under magnification these openings are described as dots.

Follicular unit. The natural grouping in which scalp hairs emerge, often more than one hair from a single opening.

Folliculitis. DermNet defines folliculitis as an inflamed hair follicle due to any cause. It often appears as a tender red spot with a pustule.

Frontal fibrosing alopecia. A scarring hair loss with recession of the front hairline. The AAD notes that it can also involve noticeable loss of the eyebrows.

H

Hair density. The number of hairs in a given area of scalp. It is observed and recorded so change can be tracked over time.

Hair pull test. A simple check in which a small bundle of hairs is gently pulled to see how many come away. See the comparison in what is trichoscopy.

Hair shaft. The visible part of the hair above the scalp. It is made of keratin and has no living cells.

Hirsutism. A male pattern of hair growth in women, for example on the face, chest or abdomen.

Honeycomb pattern. A trichoscopy term for the regular pigmented network seen on the scalp surface, mainly in darker skin types.

Hypertrichosis. Excessive hair growth over and above the normal for a person's age, sex and race. It can be present from birth or acquired.

I

Infundibulum. The upper part of the follicle, from the skin surface down to the opening of the sebaceous duct.

Inner root sheath. The inner lining of the follicle. It molds the hair shaft as it forms.

K

Kenogen. A proposed phase of the cycle in which the follicle sits empty after the old hair has been shed and before a new one appears.

Keratin. The main protein of the hair shaft. Its chains are held together in part by disulfide bonds.

Kerion. A severe inflammatory reaction to tinea capitis. DermNet describes it as a painful, boggy plaque with hair loss and pustules.

L

Lanugo. Fine, soft, unpigmented hair that covers a fetus and is normally shed before birth.

Lichen planopilaris. An uncommon inflammatory condition of the hair follicles that can lead to permanent hair loss. It is a form of scarring alopecia.

M

Malassezia. A yeast that lives on normal skin. DermNet states that its growth is believed to contribute to seborrheic dermatitis. See scalp microbiome explained.

Matrix. The cells in the bulb that divide rapidly and build the hair shaft.

Medulla. The central core of the hair shaft. It is present in coarser hairs and often absent in fine hair.

Melanin. The pigment that gives hair its color. Melanin granules sit in the cells of the cortex.

Miniaturization. The gradual shrinking of a follicle so that it produces a finer, shorter hair. It is a feature of pattern hair loss. See what is hair miniaturization.

Monilethrix. An inherited hair shaft condition that gives the hair a beaded look. The narrow segments between the beads break easily.

N

Nit. The egg case of a head louse, attached to the hair shaft. Empty cases look white and are easier to see than unhatched eggs.

O

Outer root sheath. The outer lining of the follicle. It is continuous with the epidermis and gives the follicle structural support.

P

Pediculosis capitis. Infestation of the scalp with head lice, Pediculus humanus capitis. DermNet describes the lice as small wingless insects.

pH. A measure of how acidic or alkaline something is, with 7.0 as neutral. A study in the International Journal of Trichology gives the scalp pH as 5.5 and the hair shaft pH as 3.67.

Pili torti. A hair shaft condition in which the hair is flattened and twisted at irregular intervals, making it fragile.

Pilosebaceous unit. The follicle together with its sebaceous gland and arrector pili muscle.

Pityriasis amiantacea. Thick, adherent scale that builds up on the scalp and clings to the hair. DermNet compares it to overlapping roof tiles.

Pityriasis capitis. The medical term for dandruff.

Porosity. How readily the hair fiber takes up water and products. Damaged hair, with a lifted or missing cuticle, is more porous.

S

Scalp biopsy. A medical procedure in which a physician removes a small piece of scalp for examination under a microscope. It is outside the scope of non-medical practice.

Scalp psoriasis. DermNet describes scalp psoriasis as red, thickened, well-defined patches with silvery-white scale.

Sebaceous gland. A small gland in the skin, next to the follicle, that makes and releases sebum. Cleveland Clinic notes the highest concentrations are on the face and scalp.

Seborrheic dermatitis. A common, chronic or relapsing form of dermatitis that affects areas rich in sebaceous glands, including the scalp. Scale tends to look yellowish and greasy.

Sebum. The oily substance made by the sebaceous glands. It lubricates the skin and hair and helps limit moisture loss.

T

Telogen. The resting phase of the hair cycle. Cleveland Clinic says it lasts up to 4 months.

Telogen effluvium. Excessive shedding that follows a trigger. DermNet says it occurs 2 to 6 months after an event that stops active hair growth, such as childbirth, fever, surgery or weight loss. See the telogen effluvium guide for stylists.

Terminal hair. Thick, fully pigmented hair, such as normal scalp hair.

Tinea capitis. A fungal infection of the scalp that involves both skin and hair, also called scalp ringworm. DermNet says it mainly affects children before adolescence. It needs medical care.

Traction alopecia. Hair loss caused by prolonged pulling on the follicles, often from tight hairstyles. See traction alopecia early signs.

Trichologist. In the US, a non-medical hair and scalp specialist. The title is not a state-licensed medical title. See what does a trichologist do.

Trichology. The study of the hair and scalp.

Trichoptilosis. Split ends. The cuticle wears away at the tip and the exposed cortex splits lengthwise.

Trichorrhexis nodosa. DermNet calls this the most common abnormality of hair structure. Weak points along the shaft partly fracture and look like small pale nodes.

Trichoscopy. Examination of the hair and scalp with a handheld dermoscope or a video device. See what is trichoscopy.

Trichotillomania. A disorder marked by an irresistible urge to pull out one's own hair, which results in hair loss. Also called hair-pulling disorder.

V

Vellus hair. Fine, short, usually unpigmented hair. Vellus follicles sit shallower in the skin than terminal follicles.

W

Weathering. The progressive wear of the hair fiber from root to tip. The cuticle scales lift and chip away as the hair ages.

White dots. A trichoscopy term with two uses. Small, regular white dots are a normal finding on darker scalps. Larger white areas can mark fibrosis where follicles have been lost.

Y

Yellow dots. A trichoscopy term for follicular openings filled with keratin and sebum, with no hair shaft.

What do these trichology words mean for your scope of practice?

Hair science vocabulary lets you describe, document and refer with precision. It does not change who can diagnose. A note that reads "diffuse shedding for three months, no scale, follicular openings visible" is useful to a dermatologist. A label such as "you have telogen effluvium" is a diagnosis, and that belongs to a physician.

If a client shows signs that suggest scarring, infection or sudden patchy loss, follow the steps in when to refer a client to a dermatologist. To learn this trichology terminology in a structured order, see the USTI trichology pathway.

New to the field? Start with What is trichology? or look up a term in the trichology glossary.

Sources

Frequently asked questions

What is trichology in simple terms?

Trichology is the study of the hair and scalp: how hair grows, what the fiber is made of, and what changes when the hair or scalp is not in good condition. In the US, a trichologist is a non-medical professional who observes, educates, supports with hair and scalp care, and refers medical concerns to a physician.

What is the difference between alopecia and effluvium?

Alopecia is the medical term for hair loss of any kind. Effluvium means excessive shedding of hairs. DermNet describes two forms: telogen effluvium, which follows an event that stops active hair growth, and anagen effluvium, which has a sudden onset and is linked to causes such as chemotherapy. Only a physician can diagnose either.

What are the three layers of the hair shaft?

The hair shaft has a cuticle, a cortex and a medulla. The cuticle is the outer layer of overlapping scales. The cortex makes up most of the mass of the hair and holds the melanin that gives it color. The medulla is a central core found in coarser hairs and is often absent in fine hair.

What do anagen, catagen and telogen mean?

They are the phases of the hair growth cycle. Anagen is the growth phase, which Cleveland Clinic says lasts 2 to 7 years on the scalp. Catagen is a short transition phase of about 2 weeks. Telogen is the resting phase that ends with the hair being released, which is sometimes called exogen.

What is the difference between vellus and terminal hair?

Vellus hair is fine, short and usually unpigmented, like the soft hair on the cheek. Terminal hair is thicker and fully pigmented, like normal scalp hair. In pattern hair loss, follicles gradually shrink and produce finer hairs, a process called miniaturization. A change in the mix of the two is an observation worth recording.

Is cicatricial alopecia the same as scarring alopecia?

Yes. Cicatricial alopecia and scarring alopecia mean the same thing: hair loss in which the follicle is destroyed and replaced by scar tissue. Examples include CCCA, lichen planopilaris and frontal fibrosing alopecia. Because the loss is typically permanent, any sign that suggests scarring is a reason to refer promptly to a dermatologist.

What is the difference between hirsutism and hypertrichosis?

Both mean more hair than expected, but in different patterns. DermNet defines hirsutism as a male pattern of hair growth occurring in women, such as on the face and chest. Hypertrichosis is excessive hair growth beyond the normal for a person's age, sex and race, in any pattern. Both are medical questions for a physician.

Do trichology students need to memorize medical terms?

Yes, because shared vocabulary makes observation and referral accurate. A non-medical professional uses these terms to describe what is seen and to read a physician's notes, not to diagnose. Knowing that effluvium means shedding or that cicatricial means scarring helps a stylist or barber write a clear referral summary.

This article is educational and is not medical advice. USTI teaches professionals to recognize, support and refer.

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