Got lackluster locks? Or a scaly patch on an elbow? Your body may be trying to tell you something.

"There are huge links between how we appear on the outside and what's happening inside," said Dr. Ramsey Markus, an associate professor of dermatology at Baylor College of Medicine in Houston.

Even the most common beauty woes, like brittle nails and a dull complexion, can hint at issues beneath the surface. Give yourself a once-over for these six superficial signs you should see your doctor.

If you have: Thick, dark facial or body hair It might mean: Polycystic ovary syndrome (PCOS). "We're not talking about a few wispy strands," said Dr. Zoe Stallings, a family physician at Duke Medicine in Durham, N.C. "This is a thick coat of 'I have sideburns that tweezers can't handle' hair."

It tends to sprout in places where men grow hair (like the cheeks, chin, chest and back) and may be due to elevated levels of male sex hormones—a common symptom of the endocrine disorder PCOS, which can increase your risk of infertility and diabetes. Ask your doc for a blood test.

Birth control pills and lifestyle changes like losing excess weight (even just a few pounds) can reduce symptoms. Your MD might also prescribe a steroid to help correct the hormone imbalance or a cream that inhibits the growth of facial hair. Another option: talking to your dermatologist about laser hair removal.

"The pro is that it's effective," Stallings said. "The con is the price." Each session costs around $300, though some insurance plans will cover the treatment.

If you have: A brittle nail It might mean: Fungus. It's disgusting but true—your nail bed is a perfect home for fungi.

"They like having a warm, moist layer of skin to feed off," Markus explained. When a parasite moves in, your nail may start to split or crumble at the edges. A derm might prescribe medication.

It may also help to limit exposure to moisture by wearing gloves to do the dishes or changing socks after a workout. If the nails on both hands are brittle, you can probably blame overzealous hand washing; a supplement could do the trick. Vitamins containing keratin, in particular, improve nail strength, according to a 2014 study.

If you have: A scaly red patch It might mean: Psoriasis. This rash isn't just a skin problem. Psoriasis is an autoimmune disorder that can crop up at any age and is linked to inflammation throughout the body (experts are unsure if psoriasis causes inflammation or vice versa).

Lesions—typically on the scalp, elbows and knees—are a common symptom, but moderate to severe psoriasis is also connected to cardiovascular disease, according to a longitudinal study published last fall. Fortunately, "your risk of heart attack goes down when you treat a more severe case of psoriasis," said Dr. Jennifer Chen, clinical assistant professor of dermatology at Stanford School of Medicine.

See your derm: A variety of oral and topical meds, as well as phototherapy, can reduce outbreaks.

If you have: Persistent acne It might mean: A hormonal imbalance. Breakouts aren't just for teens and tweens. "Acne may recur during perimenopause," Chen explained.

As estrogen and progesterone levels drop, your hormonal balance can tip toward testosterone, which triggers a surge in the production of pore-clogging oil. "Like menopause itself, this acne varies in duration and intensity," Chen said, though the pimples often appear on the jawline.

he good news, Chen said: "We have great medications to prevent acne. You just have to be proactive about it."

If you have: Dry, blotchy skin It might mean: An omega-3 deficiency. "As we age, our sebaceous glands produce less oil that lubricates skin," said Dr. Valori Treloar, co-author of “The Clear Skin Diet.”

Omega-3 fatty acids help keep your complexion healthy-looking in part because they protect dry skin from developing inflammation. If you have a deficiency, your skin may become itchy and blotchy, Treloar said.

Eat plenty of foods rich in omega-3s, like walnuts, flaxseed and cold water fish. Still worried you're not getting enough? Consider taking a fish oil supplement.

If you have: Thinning hair It might mean: Hypothyroidism. When your thyroid gland is underactive, too many of your hair follicles go into resting mode. As strands naturally shed, they aren't replaced, and "women start to notice that their scalp is showing," Stallings said. Synthetic hormones and other remedies can help. Another possible culprit: low estrogen.