You used to have a glorious, full head of hair. So what happened? Here are a few reasons your hair may not be as lustrous as it used to be:

First, what’s up with your diet? If you’ve stopped eating all red meat – or beans and leafy greens aren’t your thing – you may be iron deficient. And that’s linked to thinning hair. That’s according to Dr. Joshua Zeichner, a dermatologist at Mount Sinai Medical Center in New York. If you’re vegetarian, talk to your doctor about iron supplements. And be sure you're getting plenty of vitamin D, too. Low levels of D are also associated with thinning hair.

Another reason your hair may be thinning out: You blow-dry too much - or too little! A Korean study found that blow-drying damages the surface of hair, making it prone to breakage. But air-drying isn’t so hot either! Water makes hair swell and more vulnerable to damage. So putting your hair in a ponytail while wet, or sleeping with wet hair, can also break it. So use a blow-dryer on a warm or cool setting.

One final reason your hair is thinning? Serious stress… like a crisis at work, a major breakup or financial problems. The American Society of Plastic Surgeons found that women who experienced stressful events, like divorce, were more likely to experience hair loss than their twins who didn't. So find ways to manage your stress even when things are really bad.