As written before, it’s common to lose hair for about 100 hairs a day. But if you have a family history of particular hair loss condition, androgenic alopecia for example, any sign of hair loss should be concerned as well.
Androgenic alopecia is a common hair loss affecting both men and women. Below is the picture (credit to Health Wise) for the condition:
Other common causes of hair loss are as follows:
Hyperthyroidism & hypothyroidism (they are a kind of thyroid disease).
Age! Your risk of hair loss increase as you age. This is also often associated with low testosterone.
Side effects of certain medications (such as chemotherapy).
Bad diet, particularly if you have lack of iron and protein.
Bad hair care practices , such as tight ponytails /braids, combing wet hair, etc.
** Consult more with a doctor to find more advice!