See a doctor when you experience:
Gradual thinning on the top of the head
Circular/patchy bald spots
A horseshoe-shaped pattern that leaves the crown of the head exposed
Scaling of scalp
Patches of broken hairs and incomplete hair loss on the scalp and/or eyebrows
Excessive shedding of hair, but not complete baldness, after various illnesses and drug treatments, rapid weight loss or stress