We tend to regard hair only as a reflection of our personal style, but as a living, growing part of our body, it's also tied in to our physiology. "Hair reflects internal changes -- things like sickness, nutrition and stress," says dermatologist Paradi Mirmirani, M.D., a faculty member of the American Academy of Dermatology and staff dermatologist with Kaiser Permanente. There are three parts to your hair: the hair shaft (the fiber), the hair bulb (the root) and the hair cycle (the period of rest and regeneration). Most problems are related to one of these three things, says Mirmirani. Issue: Excessive hair shedding Each individual strand of hair has its own cycle, growing for six to eight years, resting for a few months, and then shedding. "About 10 percent of your hair is shedding at any one given time," Mirmirani says, pointing out that many things can interrupt the cycle and cause more hairs to shed earlier, including stress, fever, weight loss (even 10 pounds) or low iron levels. If you're noticing more shedding than usual, examine your lifestyle to see what might have changed or consult your dermatologist for tests. Issue: Hair that is dry and has lost its luster Oh, the things we do to our hair in the name of beauty, like daily blow-drying and using the flat iron. "Hair becomes dry when the cuticle starts to break down and the inner fiber is exposed," Dr. Mirmirani says. Excessive heat can cause this -- especially heat applied to wet hair. She recommends air-drying your hair partially before blow drying, only using the flat iron on dry hair, and using a daily conditioner. Remember that hair fiber with color is more prone to damage, so be extra cautious if you color-treat your hair. Issue: Hair that is dry and has lost its luster Oh, the things we do to our hair in the name of beauty, like daily blow-drying and using the flat iron. "Hair becomes dry when the cuticle starts to break down and the inner fiber is exposed," Dr. Mirmirani says. Excessive heat can cause this -- especially heat applied to wet hair. She recommends air-drying your hair partially before blow drying, only using the flat iron on dry hair, and using a daily conditioner. Remember that hair fiber with color is more prone to damage, so be extra cautious if you color-treat your hair. Issue: Split ends Split, or "dead" ends are the result of damaged or weathered hair. "The hair splays apart because the outer layer (or cuticle) of the hair shaft has worn away," Dr. Mirmirani says. But the good news is, you can snip them right off, and immediately your hair will look healthier. Another trick is to keep your ends well-conditioned. Remember there is a difference between the function of cleansing and conditioning: Shampoo is for your scalp, and conditioner is for the actual hair fibers. Issue: Gray hair The unavoidable truth is that gray hair is genetic, and aside from coloring, you're stuck with it. Most people only have a handful of hair cycles (remember, a cycle is 6 - 8 years) where the pigment-producing cells that surround the follicle and transfer pigment are working at their best. The process just gets . . . tired. Dr. Mirmirani can't confirm the old wives' tales that tell you if you yank one gray hair, five more will sprout up. However, once a fiber is gray -- even if you pluck it -- it will more than likely grow back in gray again. Issue: Dandruff Dandruff can be hereditary, but it's still a mystery what causes the flaky stuff. Daily shampooing is your first line of defense, but if the itchiness and flakes persist, try an anti-dandruff product. Dr. Mirmirani cautions sparing use of these products, however, because they are very harsh to your hair fiber. Try alternating the anti-dandruff product with regular shampoo until the dandruff clears up, and then switch back to your regular shampoo. Issue: An unexpected bald patch of hair You may have Alopecia Areata, which occurs when your immune system starts attacking the hair bulbs. It doesn't destroy it, but the bulb won't start to grow again until the attack is called off. According to the National Alopecia Areata Foundation, it affects five million people in the U.S. "It could be stress or it could be environmental factors -- we really don't know," Dr. Mirmirani says. It can happen one time or recur with some frequency. The hair can grow back though -- it's not permanent damage. If you find a sudden bald spot, see your dermatologist. Issue: Thicker hair than you've ever had before. Either you're just super lucky, or you're about to have a baby. Sure, the hormones of pregnancy can make you lose your lunch, but they are also the cause behind the thick, lustrous hair you'll probably notice if you're expecting. When you're pregnant (and for a few months postpartum), your hair stays in a high state of hair growth, with only minimal hair loss. Enjoy it while it lasts!