What can your toes tell you? The nurse just took your temperature, checked your blood pressure, and even made you step on the scale (with that heavy sweater on, no less). And as she hands you the paper gown, she gives her final directive: "You can leave your socks on."When it comes to your health, that could be a big mistake. A change in your feet--whether on the skin, nails, or even how they feel--can be the first sign of a potentially serious problem that, if caught early, could save your life. "Our feet are the first parts to be affected by nerve issues because they're the farthest from our hearts and spine," explains Carolyn McAloon, DPM, a Bay Area podiatrist and president of the California Podiatric Medication Association. Even more reason to never ignore feet: They're easily compromised when our bodies feel threatened, since we send blood to the internal organs and the brain before the extremities.Here, we reveal what could be lurking behind your most common foot concerns. If you see something familiar on the list, it's best to get it checked by your doc or podiatrist before attempting any treatment. Hairless feet and toes What it might mean: Serious circulation problems Sure, it's a pain during sandal season, but hair on your toes is a good thing. Sudden baldness can be a sign that your feet aren't getting enough blood flow to sustain hair growth. Expect your doctor to check for a pulse in your feet, which is another indication that your heart may not be able to pump enough blood to your feet, says Dr. McAloon. (Feet aren't your only cue to poor circulation. Read 8 Weird Health Tricks From Your Hands for more tips.) Frequent foot cramping What it might mean: Dehydration and nutritional deficiencies Randomly occurring cramps are about as generic as foot problems get. They can be as serious as circulation and nerve issues, or as harmless as a nutritional deficiency. If you're exercising, be sure to drink plenty of water, since dehydration often leads to muscle cramping. You might also try upping your intake of potassium, magnesium, and calcium (with your doctor's go-ahead, of course), since their deficiencies make cramps more common. "For relief, soak feet in a warm foot bath and stretch your toes toward your nose, not pointing down," says Dr. McAloon. If the cramps don't let up, see your doctor for testing to rule out circulation issues or nerve damage.A sore that won't heal What it might mean: Diabetes or skin cancer Stubborn sores are red flags for diabetes. Uncontrolled glucose levels in the blood can lead to nerve damage all the way down in your feet, which means any cut, sore, or scrape can come and go without you ever feeling it. And if it gets infected, the most serious cases may call for amputation. A non-healing wound can also be a sign of skin cancer, says Dr. McAloon. Melanoma can pop up anywhere on your body--even in between your toes--so be sure to include your feet in your regular skin checks. (Brush up on your mole-detecting skills here.)Perpetually cold feet What it might mean: Hypothyroidism Hypothyroidism is the most common cause of feet that just can't get warm. And if you're over 40, you could be living with a sluggish thyroid without even knowing it. Unfortunately, cold feet are the least of your problems--hypothyroidism can also cause hair loss, fatigue, unexplained weight gain, and depression. Get your feet feeling toasty again by heading to your doc for a simple blood test, and you'll start warming up shortly after starting the daily medication.Suddenly enlarged big toe What it might mean: Gout or other inflammatory issue "The sudden onset of a red, hot, swollen, and painful joint requires immediate medical attention," says Dr. McAloon. Typical causes include gout, inflammatory arthritis, infection, or trauma. Numbness What it might mean: Peripheral neuropathy or a pinched nerve Numbness in both feet is known as peripheral neuropathy, caused most commonly by diabetes, chronic alcoholism, or a side effect of chemotherapy. If you're experiencing neuroma, or numbness in only one foot, it could be due to a pinched nerve in the foot, ankle or back. That's most likely caused by years of wearing tight shoes (we mean you, stiletto devotees.)Bunions What it might mean: Inherited faulty foot structure If you thought your bunions were caused exclusively by a closet full of gorgeous (yet restrictive and often painful) shoes, you can stop blaming the boutique. Bunions are actually a sign of a flawed foot structure that's often inherited and merely aggravated by inappropriate shoes. "The first foot bone drives toward the middle of the body, and you see the bump," explains Dr. McAloon. It can be painful and unsightly, but the only way to really correct it is with surgery.Heel pain What it might mean: Plantar fasciitis You can't mistake it--that sharp pain in the bottom of the heel when you get out of bed or stand up from a chair. It's a strain of the ligament that supports you arch. And whether you did it by wearing too-tight shoes, walking in flip-flops, or wearing worn-out workout sneakers, the longer you let it go, the longer it takes to heal. Your podiatrist will probably tell you to ease up on your workout at first, rethink your footwear, and adopt a good stretching routine. Flaky, itchy, or peeling skin What it might mean: Fungal infection Even if you're never donned an athletic jersey in your life, you could still be walking around with athlete's foot--the euphemistic term for a fungal infection. The most common cause of itchiness and peeling, it can be treated by applying anti-fungal cream and keeping your feet as cool and dry as possible during the day. If you're fungus-free, you might be dealing with eczema or psoriasis--both to be determined by your podiatrist through a skin sample. Yellow toenails What it might mean: Fungus or pedicure overload Seeing yellow when you look down? Don't freak out--especially if you've been wearing nail polish for months on end without a break. "Yellowness can also happen naturally with age," says Dr. McAloon. If it's accompanied by brittleness or flaking, it's most likely you have a fungal infection like athlete's foot.