• Telogen effluvium is a typically reversible condition in which your hair starts falling out due to an extremely stressful event, says Bordone. Your brain tells your body to conserve energy, making your hair go into survival mode. Because your body doesn't want to spend energy on growing your hair, it reaches the telogen phase quicker, causing you to lose hair within up to three months after that stressful event.
• Androgenetic alopecia, also known as male/female pattern hair loss,
is genetic and is usually described as hair gradually thinning out, as opposed to losing a lot of hair at one time, Davis explains. Your hair follicles are gradually shrinking — due to the stimulation of the follicle by testosterone — until they ultimately shrivel and die so the hair can no longer grow.
• Alopecia areata is an autoimmune disease in which the immune system attacks the hair follicles. Davis says that this is typically characterized by losing large clumps of hair at once. Rarely, small patches of alopecia areata can progress to alopecia totatlis (total baldness) or alopecia universalis (complete loss of body hair).