Itching can be very uncomfortable. It is one of the most common reasons people see dermatologists. Itching can be triggered by wool fibers or irritants, such as solvents or cosmetics.
Itching can result from disorders that affect the skin, the nervous system (which senses itching), or other parts of the body (such as bile ducts or kidneys) or from drugs. Causes that affect more of the body than just the skin are called systemic causes.
Itching makes people want to scratch. Scratching temporarily relieves itching but can damage the skin, sometimes resulting in more itching or infection. Over time, the skin can become thick and scaly.
The most common causes of itching are related to skin disorders:
Systemic causes are less common but are more likely if there is no visible skin problem. Some of the more common systemic causes are
Less common systemic causes include an overactive thyroid gland (hyperthyroidism), an underactive thyroid gland (hypothyroidism), diabetes, iron deficiency, and polycythemia vera (a cancerous overproduction of red blood cells). Drugs can cause itching by causing allergic reactions. Drugs can also cause itching without causing an allergic reaction. For example, morphine and some radiopaque dyes given by vein (intravenously) may cause 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 causing itching are not serious.
The following may indicate that the cause could be serious:
When to see a doctor:
People who have weight loss, fatigue, or night sweats should see a doctor as soon as convenient, probably within a week or so. People with any of the other warning signs or with severe itching should probably see a doctor immediately or as soon as possible.
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 is a likely cause. If itching (usually with a rash) is confined to an area 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.
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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, either in a patch (called patch testing) or with a small needle (called prick testing).
If the cause seems not be an allergic reaction or skin disorder, testing is done based on the person's other symptoms. For example, tests may done for gallbladder or liver disorders, chronic kidney disease, thyroid disorders, diabetes, or cancer.
Disorders that cause itching are treated. Sometimes other measures can also help relieve itching.
Skin care measures can help relieve itching regardless of cause. Baths or showers should be short, no more frequent than necessary, and taken with cool or lukewarm (not hot) water. Using moisturizing soap and skin lubricants can also help, as can humidifying dry air (for example, in winter) and not wearing tight or wool clothing.
Topical treatments can be applied to the skin if only a specific area is affected. To be effective, capsaicin cream should be used for at least 2 weeks. It tends to burn, but the burning decreases over time. Menthol and camphor creams have strong odors but can be used, as can tacrolimus or pimecrolimus creams.
Corticosteroid creams can help relieve itching and often clear up the rash and other skin abnormalities in disorders such as eczema, contact dermatitis, psoriasis, and lichen simplex chronicus. Corticosteroids should usually not be used when the skin is infected, when an infestation is present, when no rash or skin abnormalities are present, and when the cause is systemic.
Type B ultraviolet light can relieve itching but can cause sunburn-like effects and increases the risk of skin cancers.
Systemic treatments are drugs that are taken internally, usually by mouth. 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. However, these drugs are usually not given during the day to elderly people, who are at higher risk of falling because of drowsiness. 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 gallbladder or liver disorders, chronic kidney disease, or polycythemia vera. However, cholestyramine has an unpleasant taste, causes constipation, and can decrease absorption of other drugs. Naltrexone can be used to treat itching caused by gallbladder or liver disorders but may increase pain if pain is present. Gabapentin can help relieve itching caused by chronic kidney disease but can cause drowsiness.
Last full review/revision December 2006 by Karen McKoy