Once, at a party, a woman said she could tell everything she needed to know about my friend by looking at her tongue. My friend dutifully opened her mouth, and after a few moments of careful examination, the woman declared that my friend needed to take control of her life.

Arguably a more impressive trick would have been to find someone who wouldn’t consider this good advice. But the idea that our tongues hold clues to our wellbeing spans millennia and continents, explains Dr Yanfang Ren, professor at the University of Rochester’s Eastman Institute for Oral Health. In traditional Chinese medicine, for example, different sections of the tongue are associated with different organs.

The shape, color and texture of a person’s tongue can offer valuable insight into their health, says Ren. “Tongues are very important for a lot of our vital functions,” Ren explains. They help us swallow, breathe, talk and do funny poses in photos.

But can a person’s tongue really convey the state of their health?

What does a healthy tongue look like?

Tongues are like snowflakes: moist. Also, no two are alike. “There is no one look for the tongue,” says Dr Frank Scannapieco, a Suny distinguished professor of oral biology at the University at Buffalo.

Generally speaking, a tongue’s color will fall somewhere between a pale pink and dark red, with a thin, white-ish layer of keratin on top. The small bumps on the surface are called papillae, which contain, among other things, one’s taste buds.

To get an idea of what your tongue’s healthy baseline is, Scannapieco recommends looking at your tongue in the mirror every so often to “get a feel for what it normally looks like”. Then, if you notice significant changes, consult with a dentist or physician.

What does a tongue’s appearance say about one’s health?

“The way the tongue looks can tell us a lot about our health,” says Jiwon Lim, staff clinician and hospital dentist at the National Institutes of Health Clinical Center. “They can tell us when our bodies aren’t working the way they’re supposed to.”

Not all changes are red flags. A tongue’s appearance will shift day to day based on what you eat and drink. Blue Gatorade will leave a distinctive bright blue residue on the tongue, for example, and that’s no reason for alarm. Coffee, tea and certain foods like berries, beets, candy and certain curries can also discolor the tongue, but only temporarily.

Discoloration could also be the result of certain medications, Scannapieco explains. “A black tongue, or a blue-ish tongue, things like antibiotics could cause that,” he says. Check with your doctor to see if these are likely side-effects of any medications you may be taking.

But certain changes may indicate more serious health concerns. Some are harmless or will go away on their own, and some may need to be treated by a dentist or physician. According to Ren, most people aren’t seeing their dentist nearly enough, and therefore don’t have a medical professional assessing the state of their tongue and mouth. “In this country, only about 40% of the population sees a dentist regularly,” he says. “That’s a problem.”

Here are some common tongue changes to keep an eye out for:

Bright red color: A bright red tongue, sometimes known as “strawberry tongue” if it’s accompanied by a bumpy texture, could signal a number of conditions, including allergies, Kawasaki disease, toxic shock syndrome, scarlet fever and a vitamin B12 deficiency.

White patches: Depending on their texture, white patches on the tongue could signal different conditions. Milky white patches that feel painful to brush or scrape could be a sign of oral thrush, says Scannapieco. This is a kind of yeast infection which is more common in babies, infants, people over 65 and those with weakened immune systems. It’s treated with antifungal medications.

If the white patches are thick and cannot be scraped off, it may be a sign of leukoplakia, which is sometimes considered a precancerous condition, says Ren.

Yellowish color: “If someone is accumulating a yellowish green debris on their tongue, that could indicate poor oral hygiene,” says Lim. This color of debris also tends to build up more in patients who smoke, she adds.

Red patches with a raised, white border: This is known as “geographic tongue”, because these spots tend to move around, appearing in different areas from one day to the next. It’s common – Ren estimates that roughly 30% of the population will experience it at some point. It’s also painless, benign and incurable. “We don’t know what causes geographic tongue,” says Lim. She says some literature points to it being an autoimmune condition, and for some of her patients, it seems to be associated with higher levels of stress.

Small sores: Small sores on the tongue or the soft tissue of the mouth are probably canker sores. These can be caused by mouth injuries (biting your own tongue, for example, or irritation from braces), stress, hormonal shifts and some allergies and food sensitivities, according to the Mayo Clinic. They may also be a sign of certain autoimmune conditions like Crohn’s disease or celiac disease.

Black color: Tongues can appear black or dark brown if the papillae aren’t shed regularly and grow longer than usual, allowing them to trap bacteria and debris in the mouth. This can cause a condition called “black hairy tongue”. It’s more commonly seen in patients who are immunocompromised, says Lim. In patients with HIV whose CD4 white blood cells are low, for example, their bodies may not be able to fight off everyday bacteria or fungi that then accumulate in the mouth.

How does one keep their tongue healthy?

“The tongue, unfortunately, is something we often ignore,” says Scannapieco.

That’s not to say you have to do a lot to keep it clean. Maintaining good oral hygiene overall is usually enough, says Lim. This means following the American Dental Association’s recommendation of brushing your teeth with fluoride toothpaste for two minutes, twice a day.

You can use a scraper, but don’t overdo it, says Lim. “If you’re scraping your tongue with too much force, it can appear fiery red or white because the papillae on our tongue have enlarged,” she explains. If you do choose to use a tongue scraper, Lim says, make sure to read the instructions and don’t apply too much pressure.

That’s one way to take control of your life – or at least your mouth.