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Itching

By

Thomas M. Ruenger

, MD, PhD, Georg-August University of Göttingen, Germany

Last full review/revision Apr 2021| Content last modified Apr 2021
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Itching can be very uncomfortable. It is one of the most common reasons people see doctors who specialize in skin disorders (dermatologists).

Itching makes people want to scratch. Scratching temporarily relieves itching but can damage the skin, sometimes resulting in more itching (the itch–scratch cycle) or infection (called a secondary infection). Over time, the skin can become thick and scaly (called lichenification).

Causes of Itching

Itching can result from

  • Skin disorders

  • Disorders of other organs (systemic disorders)

  • Disorders of the nervous system

  • Psychologic disorders

  • Drugs and chemicals

In many skin and systemic allergic disorders, itching is caused by histamine. Histamine is a chemical in the body that is stored in mast cells. Mast cells are part of the immune system, and histamine is involved in allergic reactions. When mast cells are stimulated by various allergens (substances that cause an allergic reaction), they release histamine. When histamine is released into the blood, it can cause many symptoms, including itching and inflammation. There are a number of other chemicals in the body that play an important role in itching, such as proteases and cytokines.

Skin disorders

The most common causes of itching are skin disorders:

Systemic (bodywide) disorders

Several systemic disorders can cause itch without any visible changes on the skin (such as a rash). Systemic disorders are less common causes of itch than skin disorders.

Some of the more common systemic causes are

Less common systemic causes include leukemias and lymphomas (blood cancers).

Disorders of the nervous system

Irritation of sensory nerves, for example, when a nerve is compressed, can cause itching localized to the part of the body supplied by that nerve. In contrast, some disorders that affect the nervous system may cause widespread (generalized) itching because itch neurons (one type of nerve cell) are too active or are less inhibited by other neurons. For example, in multiple sclerosis, nerve conduction is impaired because of an autoimmune process where the immune system attacks the fatty tissue that coats nerve fibers (myelin). This process makes the itch neurons less inhibited and thus more active. Itch that results from nervous system disorders is called neuropathic itch.

Psychologic disorders

Some people who have psychologic disorders may have itching for which no physical cause can be found. This type of itching is called psychogenic itching.

Drugs and chemicals

Drugs and chemicals can cause itching when taken internally or when applied to the skin. Usually the itching is caused by an allergic reaction. A few drugs, such as morphine and some radiopaque contrast agents used when taking certain x-rays, can also cause itching without causing an allergic reaction.

Evaluation of Itching

Not every episode of itching requires immediate evaluation by a doctor. The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation. Most conditions that cause itching are not serious.

Warning signs

The following may indicate that the cause could be serious:

  • Weight loss, fatigue, or night sweats may indicate a serious infection or a tumor.

  • Weakness, numbness, or tingling may indicate a nervous system disorder.

  • Abdominal pain or a yellowish discoloration of the skin and eyes (jaundice) may indicate a gallbladder or liver disorder.

  • Excessive thirst, abnormally frequent urination, and weight loss may indicate diabetes.

When to see a doctor

People who have weight loss, fatigue, or night sweats should see a doctor as soon as possible. People with any of the other warning signs or with severe itching should probably see a doctor immediately.

What the doctor does

Doctors ask many questions and look at the skin. Often, a person needs to undress so that the entire skin surface can be checked. If no clear cause is found after checking the skin, doctors may do a complete physical examination to check for systemic causes. Testing may be necessary to diagnose certain systemic causes and sometimes skin disorders.

If itching is widespread and begins shortly after use of a drug, that drug may be the cause. If itching (usually with a rash) is confined to an area that was in contact with a substance, particularly if the substance is known to cause contact dermatitis, that substance is a likely cause. However, allergic causes of widespread itching can be difficult to identify because affected people have usually eaten several different foods and have been exposed to many substances that could cause an allergic reaction before itching develops. Similarly, identifying a drug that is causing the reaction in a person taking several drugs may be difficult. Sometimes the person has been taking the drug causing the reaction for months or even years before a reaction occurs.

Table
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Some Causes and Features of Itching

Cause

Common Features*

Tests†

Skin causes

Atopic dermatitis (sometimes called eczema)

Dryness, redness, and sometimes thickening and scaling, often in the folds of the elbows or behind the knees

Usually a family history of allergies or rashes

A doctor's examination alone

Redness and sometimes blisters in a shape or location corresponding to the substance causing the reaction (such as along the hairline when caused by hair dyes, on the wrist when caused by a watch, or on exposed skin when caused by poison ivy)

A doctor's examination alone

Dry, itchy, scaly skin, usually on the legs, that is worsened by dry heat and develops or becomes worse in winter, after a hot bath, or after prolonged exposure to water

A doctor's examination alone

A circular rash with raised scaly borders

In adults, usually on the feet or genital area

In children, usually on the scalp or body

Sometimes examination of skin scales under a microscope

Hives (urticaria)

Red, raised swellings that have sharp borders and are often pale in the center

Hives go away within hours (usually less than 24 hours), but new hives continue to appear, sometimes for days to months

Usually only a doctor's examination

Sudden appearance of one or a few bumps that are usually small, red, and raised

A doctor's examination alone

Lice infestation (pediculosis)

Areas of scratched, irritated skin and sometimes tiny, pinpoint bites

Eggs (nits) and sometimes lice

Usually in the scalp, armpits, or pubic area or on the waist or eyelashes

A doctor's examination alone

Areas where repeatedly scratched skin has thickened

Areas are red, scaly, raised, rough, and separated from surrounding skin

A doctor's examination alone

Raised red patches with silver scales

Usually on the outer exposed surface of the elbows or knees or on the scalp or trunk

A doctor's examination alone

Burrows, which are small red or dark bumps, next to a fine, wavy, slightly scaly short line

Usually in the web spaces between the fingers or toes, along the belt (waist) line, on the inner surfaces of the elbows, behind the knees, around the nipples (in women), or near the genitals (in men)

Sometimes examination of skin scales or debris under a microscope

Systemic causes (conditions that affect more of the body than just the skin)

Allergic reactions that have skin and internal effects

Widespread itching

Often a raised red rash and sometimes hives

Avoiding things one at a time to see what the cause is

Sometimes skin testing

Cancer, such as Hodgkin lymphoma, certain other lymphomas such as mycosis fungoides, and polycythemia vera

Itching sometimes as the first symptom of cancer

With Hodgkin lymphoma, burning with itching, particularly in the legs

With mycosis fungoides, various raised or flat skin patches or reddening of the skin

With polycythemia vera, itching after bathing but without a rash

A complete blood count

A chest x-ray

A biopsy of lymph nodes for Hodgkin lymphoma, of skin for mycosis fungoides, or of bone marrow for polycythemia vera

Widespread itching and no rash

Sometimes worse during dialysis

Tests of kidney function

Frequent urination, thirst, and weight loss

Itching usually occurring only after other symptoms have developed

Blood and urine tests for level of sugar (glucose) and glycosylated hemoglobin (which indicates the level of blood sugar over time)

Drugs, such as aspirin, barbiturates, cocaine, morphine, penicillin, and some antifungal and chemotherapy drugs

Sometimes no rash

A doctor's examination alone

Gallbladder or liver disorders

Other symptoms of gallbladder or liver disorders, such as jaundice, fatigue, oily stools, and abdominal pain

Usually blood tests to measure liver enzymes and abdominal ultrasonography

Intense itching that comes and goes

Other symptoms of multiple sclerosis, such as numbness and tingling, weakness, loss of vision, vertigo, and clumsiness

Magnetic resonance imaging (MRI) of the brain, spinal cord, or both

Sometimes a spinal tap

Sometimes electroencephalography or electromyography

Pregnancy

Usually widespread itching without rash, developing sometimes in late pregnancy (called cholestasis of pregnancy)

Sometimes resulting from mild liver problems

Sometimes blood tests to check for a liver disorder

Psychologic factors (psychogenic itching)

Linear skin scratches and/or scabs in different stages of healing, and a psychologic disorder (such as depression or anxiety)

Tests to exclude other causes of itching, based on the person's symptoms

Thyroid disorders

With hyperthyroidism (an overactive thyroid gland): Difficulty tolerating heat, sweating, weight loss, bulging eyes, shakiness (tremor), restlessness, and sometimes an enlarged thyroid gland (goiter)

With hypothyroidism (an underactive thyroid gland): Difficulty tolerating cold, weight gain, dry skin and hair, and depression

Blood tests to evaluate thyroid function

* Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present.

† Although a doctor's examination is always done, it is mentioned in this column only if the diagnosis can sometimes be made by the doctor's examination alone, without any testing.

Testing

Most causes of itching can be diagnosed without testing. If the diagnosis of a skin abnormality is not clear from its appearance and the person's history, removal (biopsy) of a skin sample may be necessary so that it can be analyzed.

If the cause of itching seems to be an allergic reaction but the substance causing the allergic reaction is not evident, skin testing may be necessary. In skin testing, substances that can cause allergic reactions on contact are applied to the skin in a patch (called patch testing).

If the cause seems not to be an allergic reaction or skin disorder, testing is done based on the person's other symptoms. For example, tests may be done for gallbladder or liver disorders, chronic kidney disease, thyroid disorders, diabetes, or cancer.

Treatment of Itching

  • Skin care

  • Topical treatments

  • Systemic treatments

The most important aspect of treating itch is to address the cause. In addition, other measures can help relieve itching.

Skin care

If itching is caused by dry skin, modifications to basic skin care are often very effective. Dryness is often caused by excessive bathing and washing. Skin care adjustments should include bathing or washing less frequently, using lukewarm instead of hot water, and using less soap. Excessive rubbing of dry skin should be avoided, and a moisturizing cream should be applied after bathing or washing. In addition, humidifying dry air (for example, in winter) and not wearing wool clothing can also help.

Topical treatments

Topical treatments are substances that are applied to the skin, such as creams and lotions. Most topical treatments are given to address the underlying cause of the itch, for example, a doctor may give a corticosteroid cream to people who have inflamed skin resulting from atopic dermatitis or contact dermatitis.

Corticosteroid creams, lotions, and ointments should be used only when the skin is inflamed, such as when a person has a rash. They should usually not be used when

  • The skin is infected.

  • An infestation is present.

  • The cause is systemic.

Itch-relieving topical treatments that do not address a specific cause can also be given and include lotions or creams that contain menthol, camphor, pramoxine, or capsaicin. Creams and lotions that contain the antihistamine diphenhydramine or the anesthetic benzocaine are not recommended.

Exposure to ultraviolet light at a doctor's office or in the home (phototherapy) can often help lessen itchy skin disorders. It also often helps relieve itching without a rash (caused by various disorders) when other treatments are unsuccessful.

Systemic treatments

Systemic treatments are drugs that are taken internally by mouth or by injection. They are used if itching is widespread or if topical treatments are ineffective.

Antihistamines, particularly hydroxyzine, are used most often. Some antihistamines, such as cyproheptadine, diphenhydramine, and hydroxyzine, cause drowsiness. They help relieve itching and, when used before bedtime, aid in sleep. Helping people sleep is important because severe itch can affect sleep and thus greatly decrease well being. Because they can cause drowsiness, these drugs are usually not given during the day. In addition, they should also be used selectively and carefully by older people because older people are at higher risk of falling. Cetirizine and loratadine cause less drowsiness but rarely can have this effect in older people. Fexofenadine causes less drowsiness but sometimes causes a headache. Doxepin makes people very drowsy and is effective, so it can be taken at bedtime if itching is severe.

Cholestyramine is used to treat itching caused by certain gallbladder or liver disorders. However, cholestyramine has an unpleasant taste, causes constipation, and can decrease absorption of other drugs.

Gabapentin, an antiseizure drug, can help relieve neuropathic itch and itching caused by chronic kidney disease but can cause drowsiness.

Key Points about Itching

  • Itching can result from a variety of different causes, and each cause requires different treatment.

  • If the person has no rash or skin abnormalities, the cause may be a systemic disorder, a nerve problem, or a drug reaction.

  • Skin care measures (such as limiting bathing, moisturizing the skin, and humidifying the air) help relieve itching when it is caused by dry skin.

  • Itching can usually be relieved by topical or systemic treatments.

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