I know from personal experience that a series of bad hair days usually signals nothing more serious than a lousy haircut or inappropriate styling product. But: Sometimes troubles with tresses suggest an underlying health problem, according to Stefan Kuprowsky, ND, a professor at the Boucher Institute of Naturopathic Medicine in Canada — and a new stylist or styling technique won’t help when the real reason for your hair problem lies inside your body.

Dr. Kuprowsky told me, “When the 100,000 or so hairs on your head are unhealthy, chances are that you are unhealthy, too. That’s why it is important to include hair problems in your discussions with your doctor as part of an overall assessment of your health.” Here’s what you need to know if you have…

Thinning hair. An adult woman typically loses up to about 100 hairs a day, Dr. Kuprowsky said, and it is normal for this number to go up with age. Even so, no matter what your age, you should tell your doctor if there seem to be more hairs than usual in your shower drain, if your hairstyle feels skimpier than it used to or if your scalp becomes more visible — because there may be an underlying medical cause.

Possible conditions your doctor may investigate include thyroid problems… an autoimmune disorder… low iron stores in the body… starting or discontinuing birth control pills or hormone therapy… or use of certain medications, such as beta-blockers, the blood thinner warfarin or nonsteroidal anti-inflammatory drugs. Treating the underlying cause or switching medications often halts or reduces hair loss.

Also: With a condition called telogen effluvium, a sudden severe stress or shock (for instance, from a serious illness, major surgery or childbirth) triggers hair loss that begins a few weeks after the event. Fortunately, hair usually starts to grow back after about six months.

Bald patches. When clumps of hair fall out and leave bald patches, the condition is called alopecia areata. Often, women who experience this have a family history of the problem. An autoimmune disorder may be to blame. In most women, hair grows back on its own. In some cases, the condition later recurs… minimizing stress may reduce this risk.

Hair breakage. This could signal a protein deficiency. Possible causes for such a deficiency include a strict vegan diet… impaired ability to properly digest and absorb proteins and other nutrients… or low levels of stomach acid (as can occur when taking antacid medication for heartburn). Your doctor can assess your diet and medication use and order blood work and other tests to help pinpoint the problem, Dr. Kuprowsky said.

Dry hair. This suggests a dietary deficiency of omega-3 essential fatty acids. Recommended: Boost your omega-3 intake by eating more oily fish, walnuts and flaxseeds and/or by taking fish oil supplements.

Flaking, itchy scalp. This can signal an allergic reaction to hair products, so if you recently tried a new shampoo, gel or other product, stop using it and see if the flakes go away. If you also have a painful and/or inflamed scalp, see your doctor — this may signal a severe allergic reaction or chronic inflammatory condition (such as seborrheia dermatitis) that could result in hair loss.

Another possible cause for flaking is a topical yeast imbalance on the scalp, which also may be accompanied by an internal yeast imbalance in the digestive tract. This often is triggered by oral antibiotic use. According to Dr. Kuprowsky, additional possible symptoms of a yeast imbalance include excessive sugar cravings, gas, bloating, skin rashes and fatigue. To restore balance, ask your doctor about taking daily supplements of live probiotics, caprylic acid or grapefruit seed extract. If these natural yeast inhibitors aren’t strong enough, the antifungal medication nystatin, for oral or topical use, is an option. Topical help: Use an antifungal shampoo containing selenium sulfide, such as Selsun Blue.

Very oily hair. If your hair “gloms” together and you need to shampoo frequently, you might be ingesting too much saturated fat (found in meat and dairy products) or trans fat (found in many processed foods). These fats not only are unhealthy for your heart, but they also tend to make hair greasy, Dr. Kuprowsky said. His recommendation: Cut back on saturated and trans fats, focusing instead on foods with healthful unsaturated fats, such as olive oil, flaxseed oil and hemp seed oil. Your hair (and your heart) will be better for it.