If you want to take a step toward better health, see a foot doctor. You might learn something about a totally different (and seemingly unrelated) part of your body.

Sometimes, “your feet are the first place where you can see warning signs of things like diabetes or vascular disease or even skin cancer,” says Hira Mirza, a podiatrist at CLS Health in Houston. “If you look closely enough, it really is a window to the rest of your health.”

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We asked experts about the foot-related symptoms you should never ignore—and what some of these issues can reveal about your health.

Hair that stops growing on your toes

When Anne Sharkey examines patients’ feet, she always checks the hair on their toes—prompting a quizzical reaction. “They’re like, ‘Why are you looking at my hair?’ And I tell them, ‘Because if it stops growing, we have a problem,’” says Sharkey, a podiatrist in Cedar Park, Texas. It could indicate vascular insufficiency, which means the body’s veins aren’t working properly, leading to poor blood flow back to the heart. “I tell my patients that skin is like grass,” she says. “Skin needs blood to grow, grass needs water to grow, and if we aren’t getting enough blood down here, we’re not going to grow hair.”

Toe hair that’s gone MIA isn’t the only foot-related sign of a potential vascular problem. Sharkey also pays attention to changes in color, like if your toes look super pale or shiny, and temperature changes. “People come in to see us and are like, ‘My feet are really cold,’” she says. That’s a red flag for circulation problems—which are particularly common among people with diabetes—and her office helps patients get scheduled to see a vascular specialist as soon as possible.

Sudden changes in arch height or foot shape 

Women over 40 often show up in Sharkey’s office complaining of swelling and pain in one of their feet. They tell her they feel like they sprained their ankle, but they didn’t do anything that would have caused such an injury. When she examines them while they’re standing up, one foot looks normal, while the arch on the swollen one is flat.

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Many of these patients are dealing with failure of the posterior tibial tendon, which is the tendon that provides support to your arch while you’re in motion. Menopause can increase the risk: “We’re seeing a relationship between the decline in estrogen and tendon dysfunction,” Sharkey says. Patients do best when they seek treatment right away; usually, that means a combination of physical therapy, a cast or boot, and orthotics. However, “Sometimes we catch it really late because people just didn’t realize, or they thought it was a sprain and walked through it for years,” she says. “Then there’s surgeries and reconstructions to bring that tendon back to where it was.”

A red or irritated ingrown nail

Ingrown toenails are one of the most common reasons why people see a podiatrist. Yet often, they wait too long. “If you have an ingrown nail that’s red and irritated, don’t ignore it, because it’s only going to get worse,” Mirza says. “Those infections can go really wrong, really quickly.”

In addition to turning red, keep an eye out for tenderness, pain when you’re walking, drainage, or dried-up blood. Don’t try to fix the problem at home: “What happens is people unfortunately try to mess with that toenail with a non-sterile instrument or tool,” she says. “That worsens the infection, and at that point, people do end up coming in.” She typically prescribes antibiotics and does a procedure to remove the nail growing inside the skin, which turns “a three-day problem into a two- to three-week problem.”

Leg swelling that doesn’t resolve with elevation

Sudden one-sided foot or leg swelling is an emergency that can indicate deep vein thrombosis (a blood clot in the lower leg). “We need this evaluated right away,” Sharkey says. “I’ve had people walk into my office and think they ruptured their Achilles tendon because their leg was swollen, and I was like, ‘Well, your Achilles is fine, but we need to get a stat ultrasound.’”

People at particularly high risk of blood clots include those recently bedridden following surgery as well as people who traveled a long distance in a car or plane. If Sharkey is suspicious a patient has a blood clot, she sends them to the emergency room for an ultrasound and immediate treatment with clot-busting drugs.

Sudden pain in your big toe

If you wake up at night with severe toe pain, it could be a sign of gout—which Sharkey is seeing more and more in her office. The telltale symptom: a red, hot, swollen big toe that’s extremely tender and painful. “You don’t even want a bed sheet to touch it,” she says. “Patients call the office frantic in the morning, like, ‘I didn’t do anything and I woke up in the middle of the night, and I have this excruciating pain in my foot.’” They often show up to their appointment barefoot, she adds, unable to withstand the sensation of anything touching their foot.

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Gout is diagnosed through a physical exam and lab tests, and patients need steroids or oral anti-inflammatories to get their pain under control, in addition to ongoing medication management and dietary changes.

An ankle that rolls all the time

Most ankle sprains heal without triggering any long-term issues. However, 10% to 15% of people who have experienced a sprain go on to develop ankle instability, which means their foot rolls under their ankle when they do certain activities, says Dr. Travis Hanson, an orthopedic foot and ankle surgeon at Houston Methodist West. “If you saw somebody walking down the street who had an episode of ankle instability, they’d probably hop around and—depending how bad it was—maybe limp away,” he says. Many continue hobbling anywhere but to the doctor, convinced the situation will eventually resolve by itself.

That’s a bad idea: Repeatedly rolling your ankle could lead to significant problems, like torn tendons or cartilage damage. Hanson prefers to see people as soon as possible and is often able to help them strengthen their ankle with physical therapy and by improving their balance. A small percentage end up needing surgery, he adds.

An inability to pull your foot up

If you can push your ankle down—as though you were flooring it in your car—but you’re unable to pull it upwards, you may be experiencing foot drop. When this happens, “You have zero strength,” Hanson says. People tend to develop a limp, and their foot slaps so hard against the ground that “you can actually hear them as they’re walking down the hall.”

Foot drop is often caused by a pinched nerve in the lower back, but it can also be related to damage caused by knee, hip, or spine surgery. It could even be the result of the position in which you slept, in which case it usually resolves on its own within a few hours. Otherwise, after running imaging tests, doctors generally recommend treatments like physical therapy and braces, splints, or shoe inserts.

A dark streak under your toenail

Mirza recently diagnosed a patient with subungual melanoma, a rare type of skin cancer that develops under the nail bed. The telltale sign is a dark vertical line that can also lead to other color changes in or around the nail. Get in the habit of doing regular self-checks, she urges; if you typically wear nail polish, which would conceal any discoloration, check your toes before reapplying a new coat. If anything looks different than usual, schedule a doctor’s appointment.

Subungual melanoma is curable when it’s detected in an early stage. While treatment depends on the stage of the cancer, it might include removing the nail or amputating the toe in some cases. “The goal is to not have to remove the entire toe, but it depends how soon you catch it,” Mirza says.

Numbness or tingling in the feet

Sharkey’s patients sometimes show up with symptoms that indicate metabolic problems—like numbness, tingling, or burning in their feet that gets worse at night. “During the day, our body is processing so much external feedback,” she says. “At night, when things are quiet, all of a sudden your body is so much more aware.” What your body might be saying: “‘My toes are tingling, or they feel like they’re on fire,’” Sharkey says.

While people in this situation could be experiencing any type of neuropathy, the most common is related to diabetes, Sharkey adds—which is often a surprise to the patient. Foot problems are the first clue, she says, that leads to their eventual diagnosis and treatment.

Sudden onset of painless swelling, warmth, and redness of the ankle or mid-foot 

This is a commonly missed symptom among people with diabetes who have lost feeling in their feet and ankles, says Damian Roussel, a podiatrist at the Centers for Advanced Orthopaedics in Maryland. It points to a condition called Charcot neuroarthropathy, or Charcot foot, which happens when a small injury or infection makes the bones and joints start to collapse—which people overlook for a long time because of their decreased ability to feel pain.

When they finally notice redness or swelling, “They’ll usually go to their primary care doctor, and the primary care doctor sometimes assumes it’s an infection because they’re diabetic, and they’ll put them on antibiotics,” he says. “Then the patient won’t get better, and they’ll end up seeing me a month later, and no one’s done an X-ray.”

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Roussel’s imaging tests typically reveal that the bones in the middle part of the foot have started to get soft and break down. Patients with Charcot neuroarthropathy need to get off their foot entirely, he says—sometimes for a few months—to allow the bones an opportunity to heal.

An inability to bear weight on an injured foot after a few days

If you twist your ankle playing pickleball or wearing high heels, you might assume you can walk the injury off and that you’ll be back to normal soon. That might be true. But Roussel’s patients often ask him what counts as a concerning amount of pain and swelling, and how to know if they should make a doctor appointment. “I generally tell them that if you’re still not able to put weight on the foot three to four days after the injury, it needs to be seen,” he says. “That indicates a more significant injury that they probably anticipated,” such as a fracture or dislocation, or a tendon or ligament injury that requires special care.