Dear Doctor: Why is it that about four months after the baby is born a mother
loses hair. The Baganda say omwana akusekerera (loosely translated as the baby is laughing at you).

— Namisango

Dear Worried Namisango: It is true that babies may start to laugh out loud at the age of three months coinciding with the time when a mother is losing hair. Therefore, it is a logical Kiganda saying that it is the baby laughter that causes its mother to suffer hair loss.
Our heads have around 100,000 hairs and a loss of about 100 hairs a day may not significantly be noticed! Hair has a cycle whereby it grows for three to seven years, rests for about 100 days and then starts to grow again, thus the old hair is pushed out. The hormones of pregnancy keep lots of hairgrowing but unfortunately when a woman gives birth, the hair growth hormones also disappear.
That said, a lot of hair rests after 100 days (about three months) thus the old hair is pushed out resulting in noticeable hair loss. Stress of caring for a baby or acute fevers may also worsen hair loss at the time. It is important at this time to avoid plaiting as it worsens hair loss. That is the scientific explanation.