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There are hundreds of reasons why people itch, but some are more serious than others. Photo: Alamy

From diabetes to pancreatic cancer, when an itch is a symptom of something more serious

  • There are hundreds of reasons why people itch that range from simple dry skin disorders to hives, which appear after exposure to cold air or the sun
  • An itch can also be a sign of major health issues. About a third of patients suffering from end-stage kidney disease experience itching

I have an occasional “phantom” itch in the middle of my back in a place I cannot reach. I use a long-handled comb to give it a good scratch.

There’s no obvious cause – no rash, no irritation or redness, no diagnosed skin disorder. It’s annoying, but it does not disrupt my life.

Unfortunately, that is not the case for everyone who itches. About 15 per cent of the population suffers from chronic itch, according to Brian Kim, co-director of the Centre for the Study of Itch at the Washington University School of Medicine.

“It’s a very big problem,” Kim says. “Studies have shown that its impact on quality of life is equivalent to chronic pain. Many of my patients who have had both prefer pain over itch. Itch tends to be more maddening.”

Rockville, Maryland, dermatologist Thomas Keahey says itching is the chief complaint of about 20 per cent of his new patients. Also, his older patients frequently raise the issue during their annual skin cancer screenings. Most of the time their problems are minor, but “sometimes, it’s a serious request for help,” he says.

There are hundreds of reasons why people itch. These range from dry skin and such skin disorders as psoriasis, to “contact” dermatitis from rough clothing, pet dander, soaps, laundry detergents and perfume – collectively known as eczema – as well as more painfully familiar conditions such as bug bites or poison ivy.

Some people will break into hives after exposure to some external stimulus, such as cold air or the sun.

How to cure eczema naturally: by a sufferer who gave up on Western medicine

“Can you fathom breaking out with itchy hives by walking outdoors into the cold or sunlight, or following a ‘healthy’ workout?” Keahey says.

There also are unexpected causes, some of them serious. These include diabetes, kidney disease and some cancers.

Psoriasis is just one common skin disorder. Photo: Alamy

“One thing that may surprise people is that having a bad neck or back can cause itching due to damage to the nerves that come from your spinal cord,” Kim says. “Another thing people may not know is that in rare cases, cancer – particularly lymphomas and leukaemias – can present with itch.”

All-over itching caused by blockage of the bile ducts can be a sign of pancreatic cancer, for example. In cutaneous T-cell lymphoma, a type of non-Hodgkin lymphoma, the cancer begins in the white blood cells and attacks the skin, causing a chronic, itchy rash “often confused with benign forms of eczema,” Keahey says.

Also, about a third of patients suffering from end-stage kidney disease experience itching “due to a build-up of toxins, not well defined,” Keahey says.

Researchers are studying the itch-scratch cycle, trying to unravel the mysteries of what makes people itch, then scratch – and keep scratching.

Scratching causes damage to the skin, which causes inflammation, Kim says. “This increased inflammation, like with many rashes, causes more itch in a feed-forward manner,” he says. “Thus it’s a vicious ‘itch-scratch’ cycle.”

Brian Kim is co-director of the Centre for the Study of Itch at the Washington University School of Medicine. Photo: Handout

Kim and others believe the body’s immune system is a player. “We may think our immune responses end in our immune system,” Kim says. “But the itch-scratch cycle engages the immune system with the whole body, interacting with behaviour and the environment as well.”

Recent research in mice suggests there is a link between itching and food allergies, which also are an immune response.

In the animals, scratching the skin prompted an increase in the number of activated mast cells – immune cells involved in allergic reactions – in the small intestine, indicating a possible relationship between food allergies and atopic dermatitis, a type of eczema, according to a study by scientists at Boston Children’s Hospital.

At times a back scratcher is the perfect remedy for itching. Photo: Alamy

The brain also may be involved. In another mouse study, researchers at the Chinese Academy of Sciences showed that tinkering with a small subset of neurons in a brain region that processes sensory information, including pain, could prompt or halt scratching in mice, suggesting that these neurons are connected to the itch-scratch cycle.

Experts believe the cycle evolved over time among animals as a protective behaviour.

“Itch sensation plays a key role in detecting harmful substances, especially those that have attached to the skin,” one of the Chinese researchers Yan-Gang Sun, says. “As [an] itch leads to scratching behaviour, this allows the animal to get rid of the harmful substances.”

If an itch lasts more than a month, it’s probably time to see a doctor. Most people are reluctant to do so for a minor itch, and resort to over-the-counter remedies, which are too weak to have an effect, Keahey says.

“When the itch begins to affect quality of life – such as sleep – or is associated with a disfiguring rash, people will start to make their way into the dermatologist’s office,” he says.

Kim says there are numerous therapies, but the best ones depend on the nature of the itch: “Dry skin is best helped with moisturisers, whereas if you have eczema, certain anti-inflammatory drugs have better anti-itch properties than others.”

Eczema: its causes, how to get relief from the itching

As for my “phantom” itch, both Keahey and Kim believe I probably have a fairly common ailment called notalgia paresthetica, which shows up as an itch but really involves the nerves.

“We think the nerves that relay sensation from your back become damaged or dysfunctional, causing you to itch,” Kim says. “You’re right, it is a bit of a phantom itch because there’s no primary stimulation in the skin. Rather, the nerve itself is misfiring. It’s precisely what the classic ‘back scratcher’ was invented for.”

The Washington Post

This article appeared in the South China Morning Post print edition as: Why it can be irritating just to scratch the surface