Jeanine Acca used to check her hair constantly in the mirror.

Wet hair made the problem more noticeable, so she never went swimming.

“The thinning was the most difficult thing I’ve ever had to deal with,” she says.

The facts: You normally lose up to 100 hairs a day.

(Pick 20 hairs from your brush, then imagine a bunch five times larger.)

It’s also common for hair to seem a little thinner by your 40s or 50s.

“Hair helps women feel attractive and gives them a sense of self,” says Elizabeth C.W.

Hughes, clinical assistant professor of dermatology at Stanford University School of Medicine in California.

Clearly, it’s crucial to know whether hair loss is more serious than the usual hairbrush handful.

Learn the symptoms of three hair-loss conditions and what to do if one strikes your scalp.

Spotting a problem early can help you save hair and, more important, grief.

“I was shocked,” she says.

“No one warned me.”

Other triggers include iron or protein deficiency and crash dieting.

Doctors don’t know how many women suffer, but the condition is common, especially after childbirth.

To self-diagnose, tug a few sections of hair.

If you pull out more than five strands at once, telogen effluvium is probably to blame.

WHAT TO DO IF IT’S YOUBe patient.

You won’t lose enough hair that others will even notice, Dr. Miller says.

In most cases, hair returns to normal within a year.

“I thought I was just stressed,” Acca says of first losing her hair.

But the thin area became obvious.

She tried living more healthfully, quitting cigarettes and taking vitamins, but nothing worked.

“I was so desperate for a solution.

I would have sold my soul for 10 strands of hair,” she says.

WHY IT HAPPENSHalf of all women have androgenetic alopecia, a hereditary condition.

Eventually, the miniature follicles may not eke out strands at all.

You first notice a wider part or a skinnier ponytail, which can progress into obvious thinning.

This change may occur quickly or subtly over decades but will never lead to total baldness.

(Rogaine, the brand name, costs $50 for three months' worth.)

Applying the solution to the scalp twice a day regrows hair in nearly 60 percent of women.

A long, layered hairstyle can disguise thin areas and add body, and lightening your hair swells strands.

Lighter shades also create less contrast between scalp and hair.

But those fixes aren’t always effective, as Acca discovered.

She now looks as if she never lost hair at all.

During the transplant, follicles are removed and implanted one to four at a time under a local anesthetic.

Brandie Vincent, 32, was 6 years old when she got her first bald patch.

But five years ago, Vincent’s hair began falling out too rapidly to treat with injections.

In four months, all of her haireven her eyelashes and browswas gone.

“It was as if God were playing a cruel joke,” says the former hairstylist from Dallas.

She became depressed and left her job.

“I went from being a bubbly dynamo to a weepy basket case.”

Diagnosis: alopecia areata.

A saving grace is that follicles remain alive, and in the majority of cases hair regrows spontaneously.

And hair may fall out again.

Experts are waiting for more studies before passing judgment.

Many with alopecia areata wear scarves or wigs to hide bare spots.

If you’re losing hair, see a specialist.

(Find one through theAmerican Academy of Dermatology.)

“Women don’t want to admit it’s happening,” Acca says.

“But nothing compares to the distress of dealing with hair loss alone.”

Photo Credit: Alexandra Grablewski