Itching

The most common causes of itching are skin disorders:

• Dry skin (see xeroderma and ichthyosis)

• Atopic dermatitis (sometimes called eczema)

• Allergic contact dermatitis (an allergic rash resulting from direct contact with a particular substance)

• Hives (can be caused by a variety of skin or systemic conditions or drugs and chemicals)

• Fungal skin infections

• Parasitic skin infections (such as scabies)

• Insect bites

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 of itching are

• Chronic kidney disease

• Diabetes

• Disorders of the liver or gallbladder, particularly when they cause jaundice

• Hyperthyroidism (an overactive thyroid gland)

• Hypothyroidism (an underactive thyroid gland)

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

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.

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, including medications, and chemicals can cause itching when taken internally or when applied to the skin. Usually the itching is caused by an allergic reaction.

radiopaque contrast agents used when taking certain x-rays, can also cause itching without causing an allergic reaction.

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.

People who have weight loss, fatigue, or night sweats should see a doctor as soon as possible.

People who have any of the other warning signs or severe itching should probably see a doctor immediately.

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 or medication, that drug or medication 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 or medication causing the reaction for months or even years before a reaction occurs.

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.

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 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.

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

Antihistamines,

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