The most common cause of hair loss in men is “Androgenetic alopecia”, also known as “male pattern baldness”.
Androgenetic Alopecia is due to the male hormone dihydrotestosterone (DHT) that acts on the follicles making them progressively smaller until they eventually disappear. This process is called “miniaturization”.
Some other causes include:
Stress
Bacteria on the scalp
Bad nutrition
Hormonal imbalance
Injuries
High fevers caused by diseases (eg, malaria)