Physiology of hair growth

Hair on the scalp

• Grows in small clusters of 3-4 hairs per follicle unit

Hair growth

Hair follicles go through three growth phases

• Anagen – the main period of growth – lasts 3-6 years
• Catagen – slowing down (or starting up) – lasts 2-3 weeks
• Telogen – not currently growing – lasts 3-4 months

The follicle can move through this process and back again based on hormonal signalling

When anagen starts again, then the old hair is shed and a new hair starts to grow

92% of hairs are in anagen at any time.

Normally, an individual loses about 50-100 hairs per day

Signs of abnormal hair loss

• Hair on the pillow in the morning
• Clogged drain after a shower
• Hair stuck in a hair brush is NOT a significant sign and is impossible to quantify

Telogen effluvium

• Is where a greater proportion of hairs enter telogen
• Occurs after periods of stress (such as after childbirth, blood loss, high fevers, major bone fracture)
• At the time the hair loss is noted, patients are actually entering the recovery phase, as the hair follicles re-enter anagen growth phase and the old hair is being shed as a new one grows
• Can sometimes be chronic
  • Causes hairs to fall out sooner than usual (less than the normal 4 years or so)
  • Not commonly seen in men because they keep their hair short – more commonly seen in women – whereby they notice their hair is thinner as it gets longer (But hair is often thick at the scalp
• Management
  • Usually just time

Anagen effluvium

• Always abnormal. Can be caused by
  • Inflammation
  • Infection
  • Radiation

Alopecia Areata

• Non scarring
• Localised
• Often cause by tinea capitus – especially in children
  • Tinea capitus is rare in adults due to the way that adults sebaceous glands function
• Hair loss is not always complete
• Consider examining with a dermatoscope
  • Exclamation mark hairs – usually seen at the edge of an area of the alopecia. A sign of ongoing disease activity. The hair has started to grow, but this has set off inflammation around the follicle and as the hair grows, the inflammation continues and the hair becomes thinner and thinner until it falls out
  • Yellow dots (follicles without hairs) in the affected area
• May also affect the beard area
  • In men, this is a more common presentation than on the scalp. Sometimes mistaken for an area of depigmentation
• May involve the eyelashes
• Nail pits may be seen – much less obvious than those seen in psoriasis (not as deep, often from lines)
• Management
  • Topical corticosteroids
  • Corticosteroids sometimes injected intralesionally
  • Systemic corticosteroids (NOT long term) – hair often falls out again at the cessation of treatment
  • Topical immunotherapy (DCP – diphenylcyclopropenone) – is an irritant / allergen and it induces a mild contact dermatitis which stimulates hair regrowth
  • Phototherapy – PUVA
  • Laser

Diffuse, non-scaring alopecias

• No scarring – usually means that the hair follicles are not lost (initially)
  • In male pattern baldness hair follicles are lost eventually, but are often present for many years – producing fine vellum hairs before they finally die off
• Need to lose about 15% of hair until it is noticeable
• The most common cause is alopecia areata (again!)
  • Much more difficult to diagnose when it is diffuse
  • May required a biopsy
• Other causes include: telogen effluvium, anagen effluvium
• Androgenic alopecia
  • “baldness”!
  • Women actually lose hair at about the same rate as men – but they don’t lose it in a male pattern – but more generally – female pattern hairloss
  • About 25% of women have cosmetically significantandrogenetic alopecia by the age of 40
  • Hairs become thinner
  • Management of female pattern hairloss
    • No cure
    • Often just a case of slowing natural progression
    • Topical minoxidil +/- tretinoin
    • Oral antiandrogens (e.g. spironolactone e.g. 25mg – 100mg BD. Can cause menstrual irregularities at higher doses. Oral contraceptives may be an appropriate alternative. Can be used in combination with spironolactone)
    • Finasteride used occasionally but often not very effective in women
  • Management of male pattern hair loss
    • Finasteride is mainstay of treatment. Other anti-androgen are associated with a high risk of side effects
      • Need to use for 6-12 months to notice an improvement
      • 1% of patients will get gynaecomastia or impotence
      • Can be started as young as age 16
      • Be wary of FHx of early onset prostate cancer. Finasteride makes PSA unreliable
    • Minoxidil – orally 0.5mg – often compounded with spironolactone
      • Can cause excess hair growth at other sites (e.g. hairier arms and chests)
    • Topical minoxidil
      • 30% will have moderate re-growth
      • 30% will slow hair loss
      • 30% will not make any difference
      • Need to use it for more than 6 months
      • Mechanism – moves hair follicles into anagen. Follicles will only remain in anagen whilst on the minoxidil!
    • If doing a biopsy of the scalp – needs to be at least 4mm, and >1 biopsy is useful for the pathologist (and often may need >1 biopsy for a diagnosis)

Tinea Capitus

• Usually only seen in children
• Not seen in adults due to the difficult physiological functioning of the sebaceous glands in adults
• Diagnosed with a skin scraping
• Usually fairly acute onset
• Management
  • Intra-lesionsal steroid injection – very effective – but hard to perform in children
  • Topical corticosteroids and topical irritants are not very effective
  • Most cases resolve spontaneously within 6-18 months
  • Children often suffer bullying at school

Trichotillomania

• Patient pulling out own hairs
• Often unusual pattern of hair loss
• Short hairs – less than about 1cm – are very difficult to pull out, so these hairs often remain

References

• Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
• Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
• Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

Read more about our sources

Related Articles

• Acne Vulgaris
• Bullous Pemphigoid
• Bullous Pemphigus
• Burns
• Candida