Itchy skin can become a nuisance, particularly when the cause is unclear. Itchiness is usually associated with skin disorders, but it can sometimes be caused by an underlying medical condition. Infections, kidney disease, hormonal conditions and certain cancers can cause itchy skin. A thorough medical history, physical exam and special blood tests can help identify a cause and determine if additional testing is necessary.
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A number of skin disorders can cause itching, which is also called pruritus. Eczema, a condition characterized by intense itching and red, flaky skin, is one of the most common causes of itchy skin. Dry skin and psoriasis -- a skin disorder that leads to red, scaly patches -- are also frequent causes of pruritus. Allergic dermatitis causes itchiness when the skin comes into contact with particular triggers, such as detergents, soaps, cosmetic products and plants such as poison ivy. An allergic response to certain foods or medications can lead to itchy skin as well.
Many infections common during childhood, including measles, rubella and chickenpox, can cause itchy skin. All of these conditions are caused by viral illnesses and typically begin with flu-like symptoms accompanied by an itchy rash. Human immunodeficiency virus, or HIV, is another viral infection linked to pruritus. HIV can lead to itchy skin disorders, such as eczema. In some cases, though, itching may occur in people with HIV without an associated rash or obvious skin condition. Parasitic infections, like scabies and lice, characteristically trigger intense itchiness. Fungal infections, such as candida and ringworm, and bacterial skin infections due to Staphylococcus or Streptococcus can also cause itchy skin.
Cancer and Autoimmune Disorders
Itchy skin can sometimes be a symptom of cancer. Cancerous tumors of the vocal cords, breast, ovaries and digestive tract have all been associated with itching. However, generalized itchiness is most commonly linked to leukemia and other blood cell cancers. In fact, pruritus may be the first symptom of Hodgkin lymphoma, a type of cancer involving blood cells called lymphocytes, report authors of an April 2013 article in "The New England Journal of Medicine." Autoimmune disorders cause the immune system to attack a person's own organs. These disorders can lead to a number of symptoms, including itchiness. Lupus, rheumatoid arthritis and Sjogren syndrome are autoimmune conditions commonly associated with itchy skin.
Under normal circumstances, the kidneys filter a number of wastes out of the blood. Kidney failure, which can be caused by longstanding high blood pressure and diabetes, leads to an accumulation of a waste product called urea. Urea and other substances that build up in the blood due to kidney failure often cause unrelenting itchiness. In addition, people with kidney failure often note itchiness directly following hemodialysis sessions used to treat kidney failure.
Liver disorders frequently cause itchy skin. A buildup of bile, a substance secreted by the liver to help digest fatty foods, is thought to trigger itching in people with liver disease. The autoimmune disorder primary biliary cirrhosis, gallstones that block the flow of bile from the liver and viral liver infections, such as hepatitis C, are commonly associated with pruritus. Certain antibiotics, steroids and birth control pills have also been linked to liver disease and itchy skin.
Hormonal conditions, including diabetes and thyroid disease, can result in itchiness. People with diabetes are prone to skin infections and circulatory disorders that can cause itching. Disorders of the thyroid or parathyroid -- glands located in the neck that help to regulate metabolism and calcium levels, respectively -- may also trigger intense itchiness. Pregnant women often report itchy skin as well. Normal weight gain during pregnancy can provoke skin itching, as can rising estrogen levels. In rare cases, a pregnancy-related increase in estrogen can lead to bile accumulation in the liver and associated pruritus.
Neurologic disorders are often overlooked causes of itchy skin. Irritation of the nerves that normally control the itch sensation can result in chronic itchiness. A pinched nerve due to arthritis or an injury and nerve damage caused by multiple sclerosis or another inflammatory condition can lead to persistent pruritus. People who have experienced shingles, a painful rash caused by the virus that causes chickenpox, can also develop a condition called postherpetic neuralgia. Postherpetic neuralgia reflects nerve damage that usually leads to intense pain but can also cause itchiness. Brain tumors and stroke have been linked to itchy skin as well.