Alopecia is an involuntary loss of hair usually in the scalp that may occur anywhere over the body.
Scarring alopecia is severe inflammation of the hair follicle result in irreversible damage.
Non-scarring alopecias are reversible.
Alopecia may  be abrupt or gradual in onset.
Most common causes include androgenic alopecia (male & female pattern baldness) & alopecia areata.
History should be reviewed for medications, severe diet restriction, vitamin A supplementation, thyroid symptoms, concomitant illness & stress factor.