Hair
Structure
Hair consists of two parts- the hair follicle and
the hair shaft. It is composed of a protein called
keratin. Each hair strand has three layers. The
innermost layer, or medulla is found in large, thick
layer. The cortex – or the middle layer-gives
the hair its strength, colour and texture. The outermost
layer, cuticle, protects the cortex.
The hair root is enclosed within
the hair follicle, and the dermal papilla lies at
its base. The root is nourished by the bloodstream,
which helps the new hair to sprout up. This hair
follicle is influenced by the action of the male
hormones or androgens which causes it to progressively
shrink and thin down in genetically predisposed
people.
Hair growth is a cyclical process. It has three
alternating phases – Anagen, Catagen and Telogen.
Anagen ( Growing phase) lasts for 3-5 years, catagen
for 2 weeks and telogen ( resting phase) for 3 months.
The usual ratio of anagen : telogen is 12:1. Normal
hair shedding occurs in the telogen phase. The sensitivity
of dermal papilla to androgenetic hormones is increased
in alopecia patients. The increased level of androgens
lead to shortening of the anagen phase of the hair
cycle without affecting the telogen stage. As a
result of this, the ratio of anagen: telogen decreases
from the usual 12:1. Thus, the number of hair in
anagen phase ( which cover the scalp) keeps on progressively
decreasing with every cycle and telogen or the resting
hair keeps on increasing resulting in bald spots
on the scalp.
Diagram of hair structure
Distribution
of Hair
Hair is present all over the body except in the skin
of hands and feet , lips and genitals and on the end
of the fingers and toes. About five million hair follicles
are present in our skin while only 2% of them are present
on the head.
The density of hair is maximum in face (800 hairs/cm2)
followed by head, face trunk and extremities.
Causes of Hair loss
1. Noncicatricial Alopecia
Physiological: alopecia of infants, post-partum
alopecia.
Alopecia areata
Telogen effluvium
Infections: dermatophytosis, bacterial and spirochaetal
infections
Chemicals & drugs: Thallium/heparin/cancer chemotherapy/hypervitaminosis
A
Physical trauma (self induced): trichotillomania, scratching
of neurodermatitis
Endocrinopathy: Hypothyroid, hyperthyroid, hypoparathyroid,
hyperparathyroid
Physical agents: mild trauma, epilating dose of radiotherapy,
short term hair traction
Systemic diseases: systemic lupus erythematous, dermatomyositis,
sarcoidosis, langerhan’s cell histocytosis, amyloidosis.
2. cicatricial Alopecia
Physical trauma:
X-ray overdose burn, long term traction on hair
Infections:
Bacterial-leprosy, tubeculosis,
late secondary and tertiary syphilis, folliculitis decalvans,
dissecting folliculitis, carbuncles
Dermatophytosis: zoonotic fungi
Viral: herpes zoster, recurrent
herpes simplex
Chemical injury: Caustics
Cutaneous diseases: discoid lupus erythmatous, pseudopelade,
follicular lichen
planus Destructive neoplasms and granulomas
Psychogenic conditions: neurotic excoriating tactile injury
to skin
The following points are kept in mind
while evaluating the hair loss.
Rate of linear growth
Hair shaft diameter
Hair density
Hair – cycle status (anagen: telogen ratio
or %age of anagen-VI hairs)
Pigment content
History and Examination
Time period of hair loss (congenital,
acquired)
Progression of hair loss, remissions
if any (alopecia aerate may shoe remission)
Any positive family history for hair loss.
History of gastrointestinal dysfunction,
dysfunction of the thyroid gland, or psychological
disorders.
History of recent surgical intervention,
blood loss, chronic illness.
All medications Drugs, particularly
anticancer agents, anticoagulants, antoconvulsants,
thyroid drugs, ß-blockers, and trycyclic antidepressants,
can cause diffuse thinning.
