If skin were merely a sausage casing for the rest of you, it wouldn't be nearly so useful. An organ itself (your body's largest in terms of both weight and surface area), skin protects against invasive bacteria, regulates body temperature, and picks up information from the stimulation of touch, pressure, pain, heat, and cold. Little wonder, then, that when there's something wrong with you on the inside, your skin sometimes sends up the first warning flare.
"Diabetes, for example, is generally a silent disease, but it can lead to distinct changes to the skin. So the skin may in fact be the first indicator of what's happening," notes dermatologist Amy Newburger, MD, of Scarsdale, New York, a spokesperson for the American Academy of Dermatology.
Here's the skinny on ten dermatologic oddities worth watching for in yourself or someone you love.
1. Red flag: Yellowish skin, orange palms and soles
What it means: The cartoonish skin hues of carotenemia can be the unfunny result of an underactive thyroid gland -- hypothyroidism -- which causes increased levels of beta-carotene in the blood. Beta-carotene is an antioxidant, found in fruits and vegetables, that normally gets processed by the thyroid. When there's a thyroid problem, the gland doesn't metabolize the vitamins as quickly, so beta-carotene accumulates. You can also get Technicolor skin due to beta-carotene buildup thanks to a diet heavy on carrots, carrot juice, sweet potatoes, and squash.
More clues: The skin of someone with hypothyroidism also tends to be dry and cold, and sometimes more pale than yellowed. Feeling tired, sluggish, weak, or achy are the main symptoms, along with possible unexplained weight gain. Women over 50 most often develop hypothyroidism.
What to do: Carotenemia caused by a skewed diet isn't serious and resolves itself when a broader range of foods is consumed. Hypothyroidism, however, is a medical condition that can lead to such complications as heart problems, so a combination of skin changes plus fatigue warrants attention from a doctor.
2. Red flag: Breaking out in hives in the sun
What it means: Being truly allergic to the sun is pretty rare (although this kind of immune system response can happen in some people). A more likely explanation for going outside on a sunny day and coming back with an itchy rash that looks like hives or eczema is having taken a photosensitizing drug. A chemical in the medication causes changes that increase the person's sensitivity to light.
"It's common in the Northeast to have no problem all winter long, and as soon as the weather gets nice and folks are outside less bundled up, the rash appears," says Newburger.
More clues: The rash is limited to sun-exposed areas, including the forearms, the neck, and, less commonly, the face. It can feel worse and last longer than a sunburn. It doesn't matter whether you're fair-skinned or dark-skinned; anyone can have a photoreaction. One of the most common drug culprits: thiazide diuretics (Hydrodiuril, Dyazide), which are a first-line treatment for hypertension. Other meds that can produce this effect include antihistamines, tetracycline, the antiaging and antiacne drug tretinoin, and tricyclic antidepressants. Two different people can react quite differently to the same drug. Or you may have no reaction one time but a severe reaction later.
What to do: Check the labels of your prescription medications. Look for phrases such as "May cause chemical photosensitivity." Use a high-SPF sunscreen or sunblock but know that this may not prevent the rash; the best advice is to wear sunglasses and a broad-rimmed hat, cover the skin, and limit sun exposure. Tell your doctor, too; a switch in medicines may prevent further rashes.
3. Red flag: Long dark lines in the palm
What it means: A palm-reading mystic might have her own interpretation, but to a physician, a deepening of the pigment in the creases of the palms or soles is a symptom of adrenal insufficiency, an endocrine disorder. Also known as Addison's disease, the name comes from its discoverer, physician Thomas Addison. Its two most famous victims include President John F. Kennedy and -- it's thought -- the writer Jane Austen.
More clues: Hyperpigmentation may also be visible around other skin folds, scars, lips, and pressure points (knees, knuckles). Addison's sufferers have low blood pressure, which falls further when the person stands. Salt loss can lead to a craving for salty food. The disease affects men and women equally but is found most commonly between ages 30 and 50.
What to do: It's important to mention this visible symptom to a doctor, as skin changes may be the first symptoms seen before an acute attack (pain, vomiting, dehydration, and loss of consciousness, a cascade known as an Addisonian crisis). Lab tests to measure cortisol (which is produced by the adrenal gland) provide a diagnosis.
4. Red flag: Large, dusky blue leg veins
What it means: Some of your veins are no longer working properly when you spy ropy, blue-to-purple lines snaking up your legs. Venous disease -- a.k.a. varicose veins -- can be a mere cosmetic annoyance or can cause pain, cramping, and difficulty walking. Veins rely on one-way valves, like shutters, to keep blood circulating; when they stop working, blood leaks back into the vein and pools there.
More clues: Varicose veins are sometimes mistaken for spider veins, a weblike network of smaller blue or red veins closer to the skin's surface. Varicose veins tend to be larger, darker, and sometimes raised, with a twisted appearance. (The name comes from the Latin varix, or "twisted.") Half of all people over age 50 have varicose veins, especially women. They often first appear in pregnancy.
What to do: Exercise, compression stockings, and avoiding constricting postures (like crossing your legs when seated) can help ease discomfort, but they won't make varicose veins disappear. Not all faulty veins cause problems. However, if the veins cause pain or become warm and tender to the touch, tell your doctor. Severe venous insufficiency can lead to dangerous blood clots. Treatments with good success rates include sclerotherapy (injecting a solution to shut the vein) and surgery -- also options if you just can't bear how your legs look at the beach.
5. Red flag: Brownish spots on the shins
What it means: The fronts of the legs along the shins tend to bang and bump into things a lot. For someone with diabetes, the damage to the capillaries and small blood vessels that are characteristic of the disease will cause them to leak when traumatized, leading to brown discoloration known as diabetic dermopathy.
More clues: The brownish patches may also be rough, almost scaly (although they don't open up), and tend to form ovals or circles. They don't hurt. Another common skin change of diabetes to look for: An open, unhealed sore on the foot. Diabetics lose the perception of pain, temperature, and touch on their feet, making them unlikely to notice common foot blisters -- which then go untreated and may become infected.
What to do: There's no health danger from diabetic dermopathy, and no need for treatment. But if someone who hasn't been diagnosed with diabetes shows these signs, it's worth checking for other signs of diabetes, such as thirst, excessive urination, tiredness, or blurry vision.
6. Red flag: Persistent rash that you want to scratch raw
What it means: Dermatitis herpetiformis (DH) -- clusters of small, ferociously itchy blisters that show up repeatedly in the forearms near the elbows, the knees, the buttocks, the back, or the face or scalp -- are a hallmark of celiac disease, or an allergy to gluten. As many as one in four people with celiac disease have DH.
More clues: The rash appears on both sides of the body. Itching and burning are so intense you can hardly quit scratching. People with DH don't usually have the digestive symptoms of celiac disease, but they're intolerant of gluten just the same. DH often shows up between ages 30 and 40, and most often in people of northern European heritage.
What to do: Report the rashes to your regular doctor or a doctor who specializes in skin disorders to evaluate and rule out other causes. Blood tests and a biopsy of tissue from the small intestine are used to diagnose DH. A gluten-free diet for life is usually advised to keep symptoms at bay; this includes banishing foods, beverages, and medications that contain wheat, barley, rye, and sometimes oats. Drugs may help control the rashes.
7. Red flag: Purple stains or splotches
What it means: What looks a bit like a bruise, is often mistaken for a bruise, but tends to hang around longer because it's not exactly a bruise? Purpura (from the Latin for "purple"), or leaking blood vessels under the skin. It has several possible causes, ranging from a bleeding disorder to scurvy (vitamin C deficiency). But in adults over age 65, in whom it's common, the main explanation is thin skin, often made even more fragile by years of sun damage and weakened blood vessels. Then the condition is known by the unfortunate name of senile purpura.
"A substantial excessive intake of aspirin, nonsteroidal anti-inflammatories, vitamin E, or ginkgo biloba, which older adults often take to boost memory, can worsen the condition," says dermatoligst Newburger. So can blood thinners, such as coumadin, alcohol, and steroids.
More clues: A classic bruise tends to turn black and blue following an injury. With purpura, in contrast, there doesn't need to be any trauma; the discoloration starts as red and turns purple, persisting longer than a bruise before fading or remaining brownish. The purple skin doesn't blanch (fade or lose color) when you press it. Purpura can cover large patches of skin or show up as small purple speckles called petechiae. No matter what the size, the purple areas are most common on the forearms, legs, and backs of the hands.
What to do: Extensive or persistent bruises should always be evaluated by a doctor, as should someone who seems to bruise easily. It's important to rule out underlying causes such as a bleeding disorder.
8. Red flag: Intense itchiness without rash
What it means: Feeling itchy in more than one specific spot can have many causes, but when there's no accompanying visible skin change, it may be pruritis, one of the first symptoms of lymphoma (cancer of the lymph system). In fact, it's known as the "Hodgkin itch" (the two main types of lymphoma being Hodgkin's disease and non-Hodgkin's lymphoma).
More clues: The itchiness is more intense than that caused by ordinary dry skin. It can be felt generally or, most commonly, in the lower legs. Less often, the skin also looks reddish and inflamed. Another common symptom of both Hodgkin's disease and non-Hodgkin's lymphoma is swelling of the lymph nodes in the neck, armpit, collarbone, or groin. (Note that lymph nodes can swell because of common infections as well.)
What to do: Report persistent, intense itching to your doctor.
9. Red flag: Pallor, especially with blue-tinged nails
What it means: Severe anemia, a blood disorder, can show up as pasty, paler-than-usual skin on the face and palms. Anemia can be the result of iron deficiency, chronic blood loss from bowel disease, or ulcer disease, among other reasons. Iron-deficient anemia is sometimes seen in people over age 70, who may no longer prepare nutritious meals or have interest in eating them because of depression or other health problems.
More clues: Unlike merely having a pale complexion, the pallor of anemia tends to affect the usually-reddish tissues of the mouth, gums, and lips, too. Look for nail beds to be very pale, almost bluish. Other symptoms include being quick to tire, headaches, dizziness, and shortness of breath.
What to do: Consult a nutritionist or doctor. Over-the-counter or prescription iron supplements usually correct anemia caused by a nutritional deficiency. It helps to eat more iron-rich foods (red meat, egg yolks, dark leafy green vegetables, dried fruit), especially in tandem with vitamin C (as in orange juice) for best iron absorption. Cooking in an iron skillet adds iron, too.
10. Red flag: Tingling skin followed by a rash on only one side of the face or body
What it means: An often painful condition called (herpes zoster) announces itself in this distinctive way. Shingles is caused by the same virus that gives people chicken pox. In eight out of ten people who get chicken pox, the virus retreats to the body's sensory nerves and stays there. But stress, infection, certain medications (such as those used in chemotherapy and after transplants), or an aging immune system can reactivate the virus years later, producing shingles.
More clues: A burning sensation and sensitivity to touch often precede the shingles rash by days or weeks. (Or, in some lucky people, the pain may be mild.) The rash itself first looks like raised red bumps, not unlike chicken pox, appearing in a band or strip on the trunk, legs, face, neck -- but only on the left or the right side. Within a few days, the bumps turn into fluid-filled pustules, which crust over a week to ten days later.
What to do: See a doctor as soon as you feel the pain, if you suspect you're in a high-risk group. Starting antiviral medication within 72 hours of the rash's appearance can reduce the severity of the disease and lower your odds of developing a complication called postherpetic neuralgia (PHN). In PHN, the searing pain of shingles can continue for weeks, months, or even years. People older than age 70 are most likely to develop PHN, but anyone can.
And if the idea of fluid-filled pustules makes you hope you never get shingles, ask your doctor about the newish (2006) shingles vaccine, which the CDC recommends for all adults over age 60.