An average adult has approximately one lakh hair on the scalp. Hairfall is a natural part of hair growth cycle. The hair growth cycle has three phases:
- Anagen phase: It is the phase during which hair grows. It can last from three to six years.
- Catagen phase: It is a transitional phase which usually lasts for two to three weeks.
- Telogen phase: This is the phase where the hair begins to shed.
Each hair follicle is independent and goes through growth cycle at different times, else all the hair would fall at once like the way leaves fall from a tree or the way the animals shed their hair during summer. Instead, humans only shed fifty to hundred hairs a day which is absolutely normal. Scalp hair grows around 1 cm a month and the growth rate is faster in summer than in winter.
Transient hair loss may be seen after recovery from illness like typhoid and prolonged viral fever. It can also be seen after prolonged fasting, surgery and in the post-partum period after delivery of a baby. Family history, genetic disorders, hormonal factors, certain diseases, exposure to chemicals, thyroid disorders, stress, certain medications, especially those which are used for treatment of cancer may cause temporary / permanent hair loss. In addition, excessive UV exposure, exposure to hard chemicals used in hair styling results in dry, rough, frizzy, weakened and brittle hair.