To know the causes of hair loss one should know the anatomy and growth cycle of the hair.
The main purpose of hair are adornment & protection of the head from heat, cold & injury. It does not give any sense of feeling as there is absence of nerves.
Hair is mainly composed of a protein called as keratin.
Hair follicles are present all over the body except palm, soles & muco-cutaneous junctions(lip).
However over face hair shafts are very thin & shorts which are hardly visible & called as villous hair.
1) Hair root : Hair root is the part which is situated below the skin surface & is enclosed within the follicle.
2) Hair shaft : Hair shaft is that part which is extended above the skin surface.
It consists of hair follicle ,hair bulb & hair papilla.
Hair follicle is the tube like depression in the scalp encasing the hair root. There is follicle for every hair & each follicle may contain 1 to 4 hair.
Hair bulb where the actually hair growth begins ;is a thickened structure at the lower part of hair root that fits over the hair papilla.
Hair papilla is cone shaped elevation at the bottom of the hair follicle. It is rich in blood & nerve supply & helps in growth and regeneration of hair. So papilla is resposnsible for supplying nourishment to hair bulb.
Arrector pilli muscle & sebaceous or oil glands are structure connected to hair follicle. The sebaceous glands are lobulated structures that produce sebum. Sebum is secreted into sebaceous ducts that open into follicular canal. Sebum gives lustre & pliability to the hair.
1) CUTICLE : It is outside, horny, overlapping, protective layer which points away from the scalp.
2) CORTEX : This is middle layer & provides strength elasticity & contains the pigment that gives the hair its colour.
3) MEDULLA : Innermost layer .The medulla may be absent in fine & very fine hair.
Hair elasticity is the ability of the hair to stretch & return to its original form without breaking .Normal hair is capable of being stretched about one fifth of its length,however wet hair can be stretched 40 to 50% of its length.
If hair is normal & healthy each individual strand goes through a cycle of events i.e.growth, fall & replacement. Proper nourishment through food & oxygen supply by blood will cause growth of hair cells. Whenever body is ill hair papillae weaken & hair loss occurs. The growth of scalp hair occurs rapidly between the ages of 15 & 30 and declines sharply between 50 & 60. Scalp hair grows faster than hair of any other part. The normal growth rate of scalp hair is 0.3 to 0.4 mm per day or roughly 1cm per month.
1) ANAGEN PHASE OR GROWTH PHASE : Where new dermal papilla developes & bulb is formed .It accounts for 85 to 90% of hair life cycle & lasts for 2 to 6 years . ( on an average 1000 days)
2) CATAGEN PHASE OR DEGENERATIVE PHASE : It is transitional stage between the growth & inactive phases where the papillae separates from the bulb at the hair root & the bulb travels towards the skin surface .It accounts for 2 to 3 % of the phase cycle & lasts for 2 to 3 weeks ( on an average 10 days)
3) TELOGEN OR RESTING PHASE : As the hair fibre rests prior to shedding ,new hair growth begins & the cycle is completed .It accounts for 10 to 15% of cycle & lasts for 2 to 4 months (on an average of 100 days). The average life of hair ranges from 4 to 7 years however age, sex, heredity, nutrition, diseases & many other factors have effects on the duration of hair life.
Normal hair fall on an average is about 70 to 100 /day.Any increase in hair fall of more than 100 strands /day is called as considerable hair fall which may lead to appearance of bald patch ( Alopecia ).Hair can be villous hair or terminal hair.
Villous hair is thin ,small and seen on face mainly on forehead and bald area.It does not have colour as it does not contain melanin pigment.
Terminal hair is thicker,coarse and has colour due to presence of melanin pigment.Terminal hair is progressively transformed into villous hair or follicle which may later can cause baldness.
In a normal process testosterone gets converted into the dihydrotestosterone(DHT) by alpha 5 reductase enzyme .Hairs are very much sensitive to the effect of DHT.This DHT is responsible for decreasing the anagen (growth ) phase with increase in catagen ( transitional or shedding ) and telogen ( resting ) phase.This alteration of hair growth cycle by DHT is known to cause baldness.
Genetic inheritance can be from maternal (mother )side or from paternal (father) side.It can skip generation as father or uncle may not be bald.
This is autoimmune (self destructive ) disorder where T lymphocyte ( immune system)works against its own hair matrix preventing growth of new hair. This condtion is characterised by circumscribed, bald, smooth, shiny patch which may grow and become confluent with other patch forming big bald patch.
This can be due to
a) nutritional deficiency like iron,protein etc.
b) crash diet
d) drugs like o.c.pill,long term antibiotics ,antituberculous drugs,anti psychotic drugs
e) post delivery etc.
This type of baldness occurs only due to use of anticancer therapy as they (anti mitotic drugs) act on all multiplying cells and stop hair matrix division,causing no new hair growth.However the effect is reversible after stoppage of therapy.
- Hyper / Hypo thyroid
- High fever
- Diabetes mellitis etc.
- Common in turban (sikh)
- African descendants
- Hair tied tightly for regular styling.
- Brush roller alopecia
- massage alopecia
- alopecia secondary to hair weaving
- cosmetic products and procedures like colouring & straightening.
This is psychiatric condition where there is pulling and eating of scalp hair.
- Surgery ( scalp )
Apart from all above causes there are many other medical condition which give rise to alopecia or baldness.However ANDROGENETIC ALOPECIA is the commonest cause of hair loss.