The top of the head towards the posterior position, including the area at which the hair grows in a spiral pattern.

Vellus hairs are short, fine, light colored, and barely noticed, as compared with terminal hair. Vellus hair is usually less than 2 mm (1/13 inch) long and the follicles are not connected to sebaceous glands. It is most easily observed in women and children, as they have less terminal hair to obscure it. It should not be confused with lanugo, a much thicker type of hair that in humans normally only grows on fetuses.

Trichotillomania (TTM, also known as trichotillosis, or more commonly as trich) is defined as "hair loss from a patient's repetitive self-pulling of hair" and is characterized by the repeated urge to pull out scalp hair, eyelashes, facial hair, nose hair, pubic hair, eyebrows or other body hair, sometimes resulting in noticeable bald patches. Trichotillomania is classified in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) as an impulse control disorder, but there are questions about how it should be classified. It may seem, at times, to resemble a habit, an addiction, a tic disorder or an obsessive–compulsive disorder. The disorder "leads to noticeable hair loss, distress, and social or functional impairment", and is "often chronic and difficult to treat". Trichotillomania may be present in infants, but the peak age of onset is 9 to 13. Depression or stress can trigger the trich. Due to social implications the disorder is often unreported and it is difficult to predict accurately prevalence of trichotillomania; the lifetime prevalence of trich is estimated to be between 0.6% (overall) and 1.5% (in males) to 3.4% (in females)

Traction alopecia is a form of alopecia, or gradual hair loss, caused primarily by pulling force being applied to the hair. This commonly results from the sufferer frequently wearing his/her hair in a particularly tight ponytail, pigtails, or braids. It is also seen occasionally in long-haired toy dogs whose owners use barrettes to keep hair out of the dogs' faces. Traction alopecia is a substantial risk in hair weaves, which can be worn either to conceal hair loss, or purely for cosmetic purposes. The former, such as those sold in the U.S. by Hair Club, involve creating a braid around the head below the existing hairline, to which an extended-wear hairpiece, or wig, is attached. Since the hair of the braid is still growing, it requires frequent maintenance, which involves the hairpiece being removed, the natural hair braided again, and the piece snugly reattached. The tight braiding and snug hairpiece cause tension on the hair that is already at risk for falling out.

The resting phase in the hair cycle. The telogen phase is the resting phase of the hair follicle. The club hair is the final product of a hair follicle in the telogen stage, and is a dead, fully keratinized hair. Fifty to one-hundred club hairs are shed daily from a normal scalp.

The oily secretion of the sebaceous glands of the scalp, composed of keratin, fat or cellular debris.

Seborrhoeic dermatitis has been called a more extensive and severe form of dandruff. Seborrhoeic dermatitis (also Seborrheic dermatitis AmE, seborrhea) (also known as "Seborrheic eczema") is a skin disorder affecting the scalp, face, and trunk causing scaly, flaky, itchy, red skin. It particularly affects the sebum-gland rich areas of skin.

Fatty or greasy, usually referring to the oil-secrating glans of the scalp. The sebaceous glands are microscopic glands in the skin which secrete an oily/waxy matter, called sebum, to lubricate the skin and hair of animals. In humans, they are found in greatest abundance on the face and scalp, though they are distributed throughout all skin sites except the palms and soles. In the eyelids, meibomian sebaceous glands secrete sebum into tears. There are several related medical conditions, including: acne, sebaceous cysts, hyperplasia, sebaceous adenoma and sebaceous gland carcinoma.

A disease of the skin and connective tissue that can cause hair loss over the affected areas. Scleroderma is a chronic autoimmune disease characterized by fibrosis (or hardening), vascular alterations, and autoantibodies. There are two major forms: Limited cutaneous scleroderma (or morphea) mainly affects the hands, arms and face, although pulmonary hypertension is frequent. Diffuse cutaneous scleroderma (or systemic sclerosis) is rapidly progressing and affects a large area of the skin and one or more internal organs, frequently the kidneys, esophagus, heart and lungs, and can be fatal. There are no treatments for scleroderma itself, but individual organ system complications are treated.

The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly. It is usually described as having five layers. The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly.

Finasteride (marketed as Proscar, Propecia, Fincar, Finpecia, Finax, Finast, Finara, Prosteride) is an antiandrogen which acts by inhibiting 5-alphareductase, the enzyme that converts testosterone to dihydrotestosterone. It is used in benign prostatic hyperplasia (BPH) in low doses, and in prostate cancer in higher doses. It is also indicated for use in combination with doxazosin therapy to reduce the risk for symptomatic progression of BPH. Additionally, it is registered in many countries for male-pattern baldness.

The small area at the base of the hair root which provides nutrients needed for growth.

The progression of male pattern baldness is generally classified on the Hamilton-Norwood scale, which ranges from stages I to VII. This measurement scale was first introduced by Dr. James Hamilton in the 1950s and later revised and updated by Dr. O'Tar Norwood in the 1970s

Minoxidil is a vasodilator medication known for its ability to slow or stop hair loss and promote hair regrowth. It is available over the counter for treatment of androgenic alopecia, among other baldness treatments, but measurable changes disappear within months after discontinuation of treatment.

The medulla is a central zone of cells usually only present in large thick hairs. The medulla is the inner most layer of the hair shaft.

Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but un-mineralized structures found in reptiles, birds, amphibians, and mammals. They are rivalled as biological materials in toughness only by chitin. There are various types of keratins within a single animal.

Groupings of hair that grow together and share the same blood supply.

Hair transplantation is a surgical technique that involves moving skin containing hair follicles from one part of the body (the donor site) to bald or balding parts (the recipient site). It is primarily used to treat male pattern baldness, whereby grafts containing hair follicles that are genetically resistant to balding are transplanted to bald scalp. However, it is also used to restore eyelashes, eyebrows, and beard hair, and to fill in scars caused by accidents and surgery such as facelifts and previous hair transplants. Hair transplantation differs from skin grafting in that grafts contain almost all of the epidermis and dermis surrounding the hair follicle, and many tiny grafts are transplanted rather than a single strip of skin. Since hair naturally grows in follicles that contain groupings of 1 to 4 hairs, today’s most advanced techniques transplant these naturally occurring 1–4 hair "follicular units" in their natural groupings. Thus modern hair transplantation can achieve a natural appearance by mimicking nature hair for hair. This recent hair transplant procedure is called "Follicular Unit Transplantation".

A hair follicle is a part of the skin that grows hair by packing old cells together. Attached to the follicle is a sebaceous gland, a tiny sebum-producing gland found on the coxics and the putella and everywhere except on the palms, lips and soles of the feet. The thicker the density of the hair, the more the number of sebaceous glands that are found. Also attached to the follicle is a tiny bundle of muscle fiber called the arrector pili that is responsible for causing the follicle lissis to become more perpendicular to the surface of the skin, and causing the follicle to protrude slightly above the surrounding skin (piloerection). This process results in goose bumps (or goose flesh). Stem cells are located at the junction of the arrector and the follicle, and are principally responsible for the ongoing hair production during a process known as the Anagen stage. The average growth rate of healthy hair follicles on the scalp is half an inch per month.

Finasteride (marketed as Proscar, Propecia, Fincar, Finpecia, Finax, Finast, Finara, Finalo, Prosteride, Gefina, Appecia, Finasterid IVAX, Finasterid Alternova) is a synthetic antiandrogen that acts by inhibiting type II 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). It is used as a treatment in benign prostatic hyperplasia (BPH) in low doses, and prostate cancer in higher doses. A May, 2008 study indicates that finasteride reduces the rate of prostate cancer by 30%. It is also indicated for use in combination with doxazosin therapy to reduce the risk for symptomatic progression of BPH. In addition, it is registered in many countries for androgenetic alopecia (male-pattern baldness).

The Food and Drug Administration (or FDA) is an agency of the United States Department of Health and Human Services and is responsible for regulating food (human and animal), dietary supplements, drugs (human and animal), cosmetics, medical devices (human and animal) and radiation emitting devices (including non-medical devices), biologics, and blood products in the United States.

Dutasteride (marketed as Avodart, Avidart, Avolve, Duagen, Dutas, Dutagen, Duprost) is a 5-alpha-reductase inhibitor, a drug which inhibits the conversion of testosterone into dihydrotestosterone (DHT). It is used to treat conditions caused by DHT, such as benign prostatic hyperplasia (BPH).

DHT is a male hormone that is suggested to be the main cause for the miniaturisation of the hair follicle and for hair loss. DHT is formed when the male hormone testosterone interacts with the enzyme 5-alpha reductase.

The dermal papilla is situated at the base of the hair follicle. The dermal papilla contains nerves and blood vessels which supply glucose for energy and amino acids to make keratin.

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This is baldness due to scarring. The follicles are absent in scar tissue. Cicatricial alopecia presents clinically with the effacement/scarring of follicular orifices, always in a patchy or focal distribution.

Benign prostatic hyperplasia (BPH) also known as benign prostatic hypertrophy (technically a misnomer), benign enlargement of the prostate (BEP), and adenofibromyomatous hyperplasia, refers to the increase in size of the prostate in middle-aged and elderly men. To be accurate, the process is one of hyperplasia rather than hypertrophy, but the nomenclature is often interchangeable, even amongst urologists (see Textbook of Benign Prostatic Hyperplasia, Roehrborn CG et al. 2002, Chapter 6 "The Pathology of Benign Prostatic Hyperplasia, Bostwick DG). It is characterized by hyperplasia of prostatic stromal and epithelial cells, resulting in the formation of large, fairly discrete nodules in the periurethral region of the prostate. When sufficiently large, the nodules compress the urethral canal to cause partial, or sometimes virtually complete, obstruction of the urethra, which interferes the normal flow of urine. It leads to symptoms of urinary hesitancy, frequent urination, dysuria (painful urination), increased risk of urinary tract infections, and urinary retention. Although prostate specific antigen levels may be elevated in these patients because of increased organ volume and inflammation due to urinary tract infections, BPH is not considered to be a premalignant lesion.

Azelaic acid is a saturated dicarboxylic acid found naturally in wheat, rye, and barley. It is a natural substance that is produced by Malassezia furfur (also known as Pityrosporum ovale), a yeast that lives on normal skin. It is industrially produced by the ozonolysis of oleic acid. It is effective against a number of skin conditions, such as mild to moderate acne, when applied topically in a cream formulation of 20%. Azelaic acid may be useful as a hair growth stimulant.

An antiandrogen, or androgen antagonist, is any of a group of hormone receptor antagonist compounds that are capable of preventing or inhibiting the biologic effects of androgens, male sex hormones, on normally responsive tissues in the body. Antiandrogens usually work by blocking the appropriate receptors, competing for binding sites on the cell's surface, obstructing the androgens' pathway.

Androgens are often referred to as male hormones.

This is the growing phase of the hair cycle which lasts about seven years in a healthy person.

The process of converting one enzyme to another.

5 Alpha Reductase is the enzyme which converts testosterone to dihydrotestosterone (DHT) the hormone that triggers Androgenetic Alopecia in individuals who are genetically susceptible. Type 1 5-Alpha Reductase is found primarily in the skin and Type 2 5-Alpha Reductase is found primarily in the prostate and inner sheath of the hair follicle.

Alopecia Universalis is the term for hairloss which occurs over the entire body.

This is the complete loss of scalp hair often combined with the loss of eyebrows and eyelashes.

Alopecia Senilis is baldness due to old age.

Alopecia or hair loss is the medical description of the loss of hair from the head or body, sometimes to the extent of baldness. Unlike the common aesthetic depilation of body hair, alopecia tends to be involuntary and unwelcome, e.g., androgenic alopecia. However, it may also be caused by a psychological compulsion to pull out one's own hair (trichotillomania) or the unforeseen consequences of voluntary hairstyling routines (mechanical "traction alopecia" from excessively tight ponytails or braids, or burns to the scalp from caustic hair relaxer solutions or hot hair irons). In some cases, alopecia is an indication of an underlying medical concern, such as iron deficiency. When hair loss occurs in only one section, it is known as alopecia areata. Alopecia universalis is when complete hair loss on the body occurs, similar to how hair loss associated with chemotherapy sometimes affects the entire body.

Baldness following a nervous disorder or injury to the nervous system.

Hair loss baldness due to inflammation of hair follicles.

Androgenic alopecia (also known as androgenetic alopecia or alopecia androgenetica) is a common form of hair loss in both female and male humans, chimpanzees, and orangutans. In male humans in particular, this condition is also commonly known as male pattern baldness. Hair is lost in a well-defined pattern, beginning above both temples. Hair also thins at the crown of the head. Often a rim of hair around the sides and rear of the head is left, or the condition may progress to complete baldness. The pattern of hair loss in women differs from male pattern baldness. In women, the hair becomes thinner all over the head, and the hairline does not recede. Androgenic alopecia in women rarely leads to total baldness.

Acne vulgaris (commonly called acne) is a common skin condition, caused by changes in pilosebaceous units, skin structures consisting of a hair follicle and its associated sebaceous gland, via androgen stimulation. It is characterized by noninflammatory follicular papules or comedones and by inflammatory papules, pustules, and nodules in its more severe forms. Acne vulgaris affects the areas of skin with the densest population of sebaceous follicles; these areas include the face, the upper part of the chest, and the back. Severe acne is inflammatory, but acne can also manifest in noninflammatory forms. Acne lesions are commonly referred to as pimples, blemishes, spots, zits, or simply acne.