It is perfectly normal for people to shed between 50 and 100 hairs from their heads every day, according to the American Academy of Dermatology Association.

However, excessive hair loss that causes progressive thinning of the hair, bald patches, or even total hair loss can be very distressing.

There are several possible causes of hair loss. These include:

• major stressors, such as a prolonged illness, job loss, or a bereavement — this kind of hair loss is known as telogen effluvium
• some medications, including antidepressants, beta-blockers, levodopa, and chemotherapy drugs
• illnesses such as thyroid disorders, a sex hormone imbalance, or a dietary deficiency of protein, iron, zinc, or biotin, for example
• autoimmunity, which can cause hair to fall out in one or more small patches on the scalp, eyebrows, or eyelashes — this is known as alopecia areataTrusted Source
• tight hairstyles that strain the hair follicles, known as traumatic or traction alopecia
• a combination of genetics, male hormones, and increasing age, known as pattern hair loss or androgenetic alopecia; this can affect both males and females.

The biology of hair growth is complex, but in recent years scientists have made strides toward understanding how the various factors listed above cause hair loss. They hope that in time this will lead to new, more effective treatments.