Stress can be physiological or emotional and can take a toll on your hair. Physiological stresses like interim pregnancy, lactation, vitamin deficiencies, hormonal imbalances or deficiencies, surgery, sudden weight changes etc can cause hair loss. Hair loss often becomes evident few months after the actual stress. Emotional stress can also cause hair loss.
Hair loss in these cases is mostly temporary and is due to shedding of resting hair, known as Telogen Effluvium. New hair usually continues to grow.
In a normal person, about 85% of hair follicles are actively growing (Anagen hair) & rest 15% are resting hair (Telogen Hair). Anagen phase usually lasts for 3-4 years followed by a resting phase of approximately 4 months. The resting or Telogen hair has a bulb at tip and the new Anagen hair begins to grow under this resting Telogen hair and pushes it out. Therefore it is normal to lose between 50-100 hairs a day as part of the normal hair growth cycle.
When there is any stress/ shock to the body, as many as 60-70% of Anagen hair can go into the resting phase, thus reversing the ratio and causing Telogen Effluvium. It is only about 2-4 months r the shock that the new hairs push out the resting hair clubs (Telogen Hair) & increased hair loss is noticed some months after the initial shock.
Covid infection is also a significant physiological stress and can cause stress related hair loss or Telogen Effluvium.