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Hair loss

Author: Honorary Associate Profesor Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1998. Further updates: December 2015 and May 2023.


What is hair loss?

The medical term for hair loss is alopecia. There may be associated scalp disease or scarring.

  • Alopecia may be localised or diffuse.
  • It can affect the scalp or other parts of the body.
  • It may be due to hair shedding, poor quality hair, or hair thinning.
  • There may be areas of skin that are completely bald.
  • There may be associated skin disease or scarring.

Unfortunately, hair loss may not be easy to remedy.

Who gets hair loss?

As all our hair follicles are formed during fetal growth, it is inevitable that we will notice hair loss of some kind in later life.

Hair loss occurs in:

  • Males and females
  • Children and adults
  • People with any colour or type of hair.

Hair loss can be an isolated problem or associated with another disease or condition. It can be temporary or permanent, depending on the cause.

How does hair grow?

Hair grows on most parts of the skin surface, except palms, soles, lips and eyelids. Hair thickness and length varies according to the site.

  • Vellus hair is fine, light in colour, and short in length
  • Terminal or androgenic hair is thicker, darker and longer

A hair shaft grows within a follicle at a rate of about 1 cm per month. It is due to cell division within the hair bulb at the base of the follicle. The cells produce the three layers of the hair shaft (medulla, cortex, cuticle), which are mainly made of the protein keratin (which is also the main structure of skin and nails).

Hair growth follows a cycle. However, these phases are not synchronised, and any hair may be at a particular phase at random.

The three main phases of the hair cycle are:

  1. Anagen: actively growing hair, most of them
  2. Catagen: in-between phase of 2–3 weeks when growth stops and the follicle shrinks, 1–3% of hairs
  3. Telogen: resting phase for 1–4 months, up to 10% of hairs in a normal scalp.

Hair length depends on the duration of anagen. Short hairs (eyelashes, eyebrows, hair on arms and legs) have a short anagen phase of around one month. Anagen lasts up to 6 years or longer in scalp hair.

Hair cycle

Image © 1998 Merck Sharpe and Dohme (with permission)

What causes hair loss?

Hair loss can be due to:

What are the clinical features of hair loss?

The features of hair loss depend on the cause. Actual symptoms such as itch and soreness are generally absent unless caused by accompanying inflammatory skin disease. However, a burning, prickly discomfort known as trichodynia may accompany hair shedding.

Anagen hair loss

Anagen hair is tapered or broken-off. Anagen is variable in duration. Children with otherwise normal hair but that cannot grow their hair long may have short anagen syndrome.

Anagen shedding is known as anagen effluvium and has a sudden onset.

Anagen effluvium is caused by:

Short broken hairs and empty follicles may be observed. If caused by a drug or toxin, hair growth can return to normal within 3–6 months of its withdrawal.

Anagen hair loss

Telogen hair loss

Telogen hair has a bulb at the end (club hair). Excessive shedding is known as telogen effluvium. It occurs 2–6 months after an event that stops active hair growth.

Telogen effluvium is caused by:

Sometimes there appears to be no recognisable cause for telogen effluvium, and shedding can continue for years (chronic telogen effluvium). Scalp hair continues to grow but has a shorter natural length than normal.

Telogen effluvium

Pattern hair loss (androgenetic alopecia)

Pattern hair loss is due to genetic programming or hormonal influences. It is also called androgenetic alopecia because it is influenced by androgens.

Pattern alopecia is apparent in about 50% of individuals by the age of 50 years.

Pattern balding

Hair shaft abnormalities

Hair shaft defects can be inherited and congenital, or acquired due to disease or injury (eg, excessive brushing, hair pulling [trichotillomania], hairdryer heat, relaxing chemicals, bleach). See African hair practices.

Hair shaft abnormalities are diagnosed by dermatoscopy or microscopic examination of the hair, and sometimes by scanning electron microscopy. They include:

  • Fractures: trichorrhexis nodosa, trichoschisis, trichoclasis (trichothiodystrophy)
  • Irregularities: trichorrhexis invaginata (seen with ichthyosis in Netherton syndrome), Marie-Unna hypotrichosis (uncombable hair), pili bifurcati, pili annulati, pseudopili annulati, monilethrix (beaded hair), pseudomonilethrix
  • Coiling and twisting: pili torti (twisted hair), woolly hair, trichonodosis (knotted hair).

Dermatological disease

Conditions resulting in reversible patchy hair thinning, poor hair quality and bald patches include:

Hair loss due to scalp conditions

Systemic disease

Systemic diseases resulting in reversible patchy hair thinning, poor hair quality and bald patches include:

Destructive inflammatory skin diseases

Inflammation in the dermis or subcutaneous tissue may injure the hair follicle resulting in localised bald patches in which there are no visible follicles; this is called scarring alopecia or cicatricial alopecia.

Traumatic causes of scarring alopecia may be due to:

Traumatic forms of alopecia

Infections causing scarring alopecia include:

Inflammatory skin diseases causing scarring alopecia include:

Pseudopelade of Brocq is a condition in which there are localised areas of the scalp in which hair follicles have disappeared without visible inflammation.

Scarring alopecia

Complications of hair loss

Whatever the type of hair loss, it may be extremely distressing and embarrassing, reducing the quality of life and causing psychosocial problems. Loss of normal scalp hair increases the risk of:

How is hair loss diagnosed?

A careful history and full skin examination can generally result in the correct diagnosis. Additional tests may include:

  • Hair pull test to determine the relative proportion of anagen and telogen hairs
  • Wood lamp examination
  • Swabs of pustules for bacterial and viral culture
  • Skin scrapings and hair clippings for mycology
  • Blood tests for haematology, thyroid function, serology.

What is the treatment for hair loss?

Treatment depends on the diagnosis.

  • Infections should be treated.
  • Deficiencies should be remedied.
  • Causative drugs may be discontinued.
  • Inflammation can be suppressed.
  • Treatment may be available for specific conditions.

A systematic review of 30 studies suggests a discussion on nutritional supplementation should be considered between patient and physician.

How can hair loss be prevented?

Most types of hair loss cannot be actively prevented. However, it is prudent to avoid injury to the hair shaft.

  • Dry hair naturally or with a hairdryer on a cool setting
  • Minimise chemical treatments or use them infrequently
  • Use loose hairstyles to avoid traction injury 

What is the outlook for hair loss?

The outlook for hair loss depends on the diagnosis. Scarring alopecia is permanent.

  • Anagen and telogen shedding generally stops in time
  • Early treatment of pattern alopecia may reduce the speed of thinning
  • Treatment of any inflammatory disease may be successful
  • Hair loss can be disguised or covered
  • Hair replacement techniques include wigs, hairpieces and surgery.



  • Diagnosing and Treating Hair Loss – Am Fam Physician. 2009 Aug 15;80(4):356-362.
  • Drake L, Reyes-Hadsall S, Martinez J, Heinrich C, Huang K, Mostaghimi A. Evaluation of the Safety and Effectiveness of Nutritional Supplements for Treating Hair Loss: A Systematic ReviewJAMA Dermatol. 2023;159(1):79–86. doi:10.1001/jamadermatol.2022.4867 Journal 

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