Itching is arguably the most universal symptom known to humans. It is a rare person who at one time or another has not scratched an itch.

Some itches are mild, and others are maddeningly severe, affecting sleep and lifestyle. Fortunately, most—such as those caused by insect bites and contact allergies due to poison ivy, fabrics, cosmetics, and the like—improve or disappear within a short period of time.

But some itches do become chronic (lasting longer than six weeks) and are more perplexing, possibly requiring a skin biopsy for diagnosis. In one large published survey of Norwegians, about 8 percent suffered from chronic itching. An even higher prevalence (17 percent) was found in a published survey of German workers.

Different itches require different tactics to subdue them. But most important to the sufferer is to know when it’s time to seek medical advice.

If You’re Itchy All Over

Generalized itching commonly affects older adults as a result of dry skin, also known as xerosis. That becomes a problem in winter, when indoor heat reduces humidity and dries the air. As we age, skin loses the precious sweat glands that exude protective oils, and a dry environment magnifies the problem.

Proper self-treatment can save the day. Avoid excessive contact with water, which washes away what little oil remains on the skin surface. Take tepid (never hot) showers instead of baths, and limit showers to only a few minutes. Afterward, apply a skin-protective emollient lotion, such as Vaseline Intensive Care. You can use the emollient several times per day on exposed parts of the body.

But if the itch doesn’t yield to self-­management, check with your doctor—the cause may be of more concern. Anemia, or thyroid, liver, or kidney disease, can be accompanied by itching. At times, itching can be the tip-off to the presence of cancer—most commonly a lymphoma or another type of internal malignancy.

When the Itch Is Limited

Localized itching (confined to one or two areas) is usually due to an itch-scratch-itch-scratch cycle that takes place over a period of months or even years. The repetitive scratching leaves a thickened, even itchier patch of skin, which is often slightly darker than the surrounding area. The initial cause of the itch is usually forgotten with the passage of time.

To break that distressing cycle, you may need a topical over-the-counter cream containing capsaicin (Zostrix and generic) or lidocaine, or a prescription cream containing doxepin (Prudoxin, Zonalon) or a corticosteroid. And resist the urge to scratch! Clipping your nails helps, as can covering the area with gauze or a bandage.

Have a Rash, Too?

Generalized itching accompanied by a rash is probably the least amenable to self-help measures and the most frequent reason for seeking professional advice. Although myriad itchy skin rashes without a known cause abound, drug reactions constitute a large portion, and the most common offenders are antibiotics, notably penicillin and sulfa drugs.

Foods are also a major cause of itching, with shellfish at the top of the menu, and infection is likely if you have a fever along with an itchy rash.

Another common cause is the auto­immune condition psoriasis: Only one in five people with it escapes without severe itching. An old remedy, sunlight, is helpful, as is a new class of prescription drugs known as tumor necrosis factor (TNF) antagonists.

Localized itching with a rash is most often set off by insect bites or fungal infections. Fungi thrive in areas that are dark, moist, and warm, such as the armpits, feet, groin, and under the breasts. Common and uncomfortable manifestations are athlete’s foot, jock itch, swimmer’s ear, and ringworm. Anal and vaginal itching can be especially troublesome, if not downright embarrassing.

For all of the above, many OTC preparations such as clotrimazole and miconazole are available. But they are rarely totally successful, and professional attention might be needed for diagnosis and targeted treatment.

Mosquito or “no-see-um” bites usually require only a cold compress or a dab of OTC hydrocortisone cream. But spider bites can turn ugly when they ulcerate and become infected, requiring antibiotics and professional wound care. Bee stings usually resolve on their own (the stinger should be removed) and need medical attention only when the area of itching and redness extends well beyond the bite site.