You know when someone goes on a temporary "cleanse" (read: doesn't eat solid foods to fit into that dress) and the starvation mode argument naturally arises -- i.e., when you don't eat, your body thinks you're starving and holds onto any fat it can find? The same logic can be applied to the relationship between your protein intake and your hair. When you skimp on protein, your body rations off any remaining sources of it in the body so that it can be used toward more essential bodily functions. That means your 150,000 strands (give or take) get pushed to the back of the soup line. A lack of protein tells the body to pull the plug on way more hair follicles than usual by pushing them into the "resting" phase.

Solve It:
That protein bar you had during your lunch break isn't going to cut it. Adult women need about 46 grams of protein a day, and if you're pregnant or lactating, the recommended intake jumps to 71 grams a day. For meat eaters, this means making sure you're getting an adequate amount of meat, fish and dairy into your meals. Vegetarians should make sure they're getting protein in the form of beans, whole grains, nuts and eggs.

We're obsessed with popping multivitamins (or chewing the gummy versions) but as with most things in life, you can have too much of a good thing. Overdoing it on supplements containing vitamin A can actually trigger hair loss, Marotta explains, and if you look at the supplements in the grocery story aisle, it's disturbingly easy to sabotage your head of hair. "The daily value for vitamin A is 5,000 International Units (IU) per day for adults," he says. But supplements can contain anywhere from 2,500 to a whopping 10,000 IU.

Turns out, not getting enough vitamin D may be just as bad as overdoing vitamin A. Researchers at Cairo University found that women who experience hair loss had lower levels of D ... and the hair loss only worsened as the levels dropped.

Solve It:
Researchers still aren't completely sure of the role vitamin D plays with hair follicle growth, but women should aim for a minimum of 600 IU of vitamin D per day. Good sources of the vitamin include fortified milk and orange juice, and salmon. As for the vitamin A issue, double-check your supplement labels.

It's tempting to rake through tangles and secure the tightest top knot known to man, but vigorous styling and hair treatments add up, and yes, they can cause your hair to fall out. If you get a mild headache every time you pull your hair back into a ponytail, you need to ease up for your hair's sake. "Tension, stress and pulling on hair follicles and the scalp can lead to a form of gradual hair loss called traction alopecia," says Leonard. This can be anything from "tugging" styles (think tight braids, hair weaves, corn rows) to harsh chemical treatments like relaxers and perms -- not to mention basically every hot tool on the market.

Solve It:
The American Academy of Dermatology recommends using conditioner after shampooing and using hot styling tools only once a week. If that sounds laughable, try to give your hair a break once in a while -- especially if you are seeing an increase in hair loss. Leonard also recommends rethinking the way you comb through fragile, wet hair. "Be sure to comb from the ends, back to the scalp, and don't rip through tangled snarls." We'll also add, invest in a good de-tangler, like Joico's, $11.99, to decrease the stress on your strands when combing.

Do you find yourself scratching your scalp on the regular? If the breeding ground for your hair isn't in the best shape, your follicles have no chance of thriving. "An unhealthy scalp often leads to inflammation, which makes it difficult for hair to grow," says Marotta. Skin conditions that cause itchy, flaky and red scalps, such as seborrheic dermatitis (better known as dandruff), psoriasis, sunburn and fungal infections can all contribute to hair loss in this way.

Solve It:
If you suffer from dandruff, pick up a dandruff shampoo, but if the itching and redness get serious, head to a dermatologist or trichologist for a more potent solution. In the meantime, celeb stylist Diane C. Bailey recommends regular scalp massages to increase blood flow to the scalp. "This helps nutrients travel to follicle sites where hair cells are reproduced." Bailey recommends choosing a hair oil that contains tea tree, (like Wen Tea Tree Oil, $20) baobab, peppermint, rosemary, or ylang-ylang oils, all of which stimulate and soothe the scalp. Massage all over your scalp with the pads of your fingers for three minutes, then shampoo out.

After menopause, about 40 percent of women experience hair thinning, which is almost the same rate of hair loss in men. Women, however, tend to thin out all over, rather than develop the signature male pattern baldness. Fluctuations in hormone levels are definitely to blame, though many of the other hair loss causes we've discussed (genetic predisposition, unusual levels of stress, vitamin deficiencies) also make a more notable appearance at this point in a woman's life.

Solve It:
According to hair loss specialist Dr. Alan Bauman, this type of hair loss can't be cured with hormone replacement alone. "Most women benefit from a combination of pharmaceutical and lifestyle changes, but results are always proportional to the patient's level of discipline." Bauman suggests treatments and ingredients "that protect and enhance hair follicles," such as compounded topical minoxidil, found in Keranique, $30, a hair regrowth treatment designed specifically for women, Formula 82M, platelet-rich plasma injections, Bimatoprost (the active ingredient in Latisse), low-level laser therapy. He's also a fan of nutritional supplements like Viviscal, $49.99, and pharmaceutical grade biotin.