While treatments for male pattern baldness are continually developing, another hair-related condition is still not well understood.

Amy, who didn't want her last name published, was 18, just finishing her freshman year of college in Sioux Falls, S.D., when she discovered a bald spot the size of a quarter on the back of her head.

"It was pure bald; it was so smooth," said Amy, now 23 and living in Chicago. "I was freaking out, thinking I was totally going bald."

She had alopecia areata, and she could have gone bald -- some people with the condition do. It's considered an autoimmune disease, meaning the immune system attacks hair follicles, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

While alopecia areata isn't a life-threatening disease, its effects can be psychologically trying. In most cases, hair falls out in small, round patches, and often doesn't extend beyond a few bare spots. But some people have more extensive hair loss -- including total baldness or complete loss of hair on the head, face and body.

The condition affects about 4 million Americans, both male and female, of all ages and ethnic groups, usually beginning in childhood, according to the NIAMS.

Fortunately, the follicles always have the potential to regrow hair, which is what happened in Amy's case. She visited one doctor who told her she might very well go bald.

"That experience was really bad," she said.

Then she went to a dermatologist who prescribed Rogaine for men -- which is stronger than that designed for women. To her relief, her hair grew back in a matter of months.

"I haven't had anything since then," Amy said. "They would tell me lots of times it's stress-related, or maybe it's hereditary."

But she said she doesn't know of any family members who have had the condition, and she's been under much more stress than she was then without the same results.

The NIAMS says the condition is unpredictable -- the hair may regrow, but it may also fall out again. There isn't a cure for the condition, nor any drugs approved specifically to treat it.