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HAIR IN HUMANS AND PETS

First broadcast on www.provet.co.uk  


This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

All mammals have hair and suckle their young with milk....but there are big differences between the hair that different species have.

The most obvious difference between human and pet hair covering is the distribution - humans are only partly covered with hair, whereas cats and dogs are generally covered all over - except for some breeds of dog including the Chinese Crested Dog and the Mexican Hairless Dog. In certain areas the hair covering is usually thinner than others - eg the underside of the abdomen is usually only sparsely covered in hair.

Hair is important for :

  • Insulation against environmental temperature - depends on the depth of still air trapped by the hair. The amount of insulation  is governed by the hair length, thickness, density and the medullation* of individual hairs. 
  • Sensory perception - due to movement of the hairs
  • Protection against :
    • Physical damage
    • Chemical injury, and
    • Microbiological infections
  • Camouflage
  • In humans and some breeds of dog hair style is an important social and fashion accessory

(*A hair with a medulla has a hollow centre)

Most species of mammal have two types of hair which are medullated:

  • Primary (outer coat) hairs , and
  • Secondary (down or undercoat) hairs

Hair growth and replacement have been studied in many mammals and hairs grow in cycles rather than continually :

  • A growing period (anagen)
  • A resting period (telogen) - these hairs are dead and are eventually shed to be replaced by new growing hairs, and a
  • A transitional period (catagen) between these two phase 

The cycle varies from one animal to another - and the duration of each stage of the cycle depends upon :

  • Genetic inheritance - there are species and breed variations
  • Age
  • Photoperiod (hours of daylight)
  • Environmental temperature
  • Hormonal changes
  • Nutrition
  • Variations in hair follicle activity - higher in warm climates
  • The anatomical location of the hairs
  • General health status of the individual

In cats and dogs hair is replaced in a mosaic fashion as different adjacent hair follicles are in different stages of their cycle.

Dogs and cats that shed excessively may have a disorder in their hair growth cycle or may be responding to abnormal environmental conditions or other stimuli that increase the rate of the resting phase of the hair growth cycle with subsequent shedding. Also poor nutrition or ill health can lead to poor hair condition and excessive shedding.

Excessive hairloss due to dead hair falling out must be differentiated from hairloss due to self-trauma or diseases such as ringworm.

 

Updated October 2013