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What are the causes of alopecia?

Alopecia is the loss of hair from skin. It is of 2 types
Non-cicatrical alopecia and Cicatrical alopecia 
Causes of Non-cicatrical alopecia 
Physiological alopecia also called as male pattern of alopecia
Physiologic androgenic alopecia is an autosomal dominant male pattern of baldness,there is bitateral pattern of hair loss and is usually familial. 5-alpha reductase inhibitor finasteride is useful in the treatment. Other causes are puberty, pregnancy and neonatal period.
Alopecia areata is the most common type of noncicatricial alopecia.It is a autoimmune disease characterised by single or multiple areas of alopecia without any inflammation.
If it involves the whole of the scalp it is called atopecia totatis 
If it involves the whole of the body it is called atopecia universalis
It is associated with other auto immune disease like  SLE, vitiligo, autoimmune haemolytic anemia
Systemic diseases that produce alopecia are 
  • SLE
  • Hyperthyroidism
  • Hypothyroidism
  • Acrodermatitis enteropathica
  • Pernicious anemia 
  • Down's syndrome.
Infection: Moth eaten type of alopecia is seen  in syphilis and fungal infections.
Drugs: Antimetabolites, Cytotoxic agents, Carbimazole, Iodine, Bismuth, Vitamin A and Amphetamines. 
Telogen effluvium: is the hair loss following systemic illness (typhoid, measles, pneumonia) postpartum and postsurgical cases.
Alopecia in females  seen in virilising tumor of ovary or adrenal
Causes of cicatricial Alopecia
It is due to primary dermatological conditions
  • Trauma
  • Burns
  • Folliculitis, gumma, lupusvulgaris and herpes zoster
  • Morphea, lichen planus, saroidosos and DLE
  • Drugs-Mepacrine.
Decreased Body Hair Distribution (Loss of Secondary Sexual Character)
This is seen in the following conditions:
  • Decompensated liver disease
  • Klinefelter's syndrome
  • Bilateral testicular atrophy as seen in Hansen's disease.