Itching

We have selected the following expert medical opinion based on its clarity, reliability and accuracy. Credit: Sourced from the MSD Manual, Consumer Version; authored by Dr Mercedes E. Gonzalez (see below). Please refer to your own medical practitioner for a final perspective, assessment or evaluation.

Overview

Itching can be very uncomfortable and is one of the most common reasons people see doctors who specialize in skin disorders (dermatologists).

Itching makes people want to scratch. Although scratching temporarily relieves itching, it can also 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

Itching can result from:

• Skin disorders (most common cause)
• Disorders of other organs (systemic disorders)
• Drugs and chemicals

Skin disorders

The most common causes of itching are skin disorders:

• Dry skin (conditions called “xeroderma” and “ichthyosis”)
• Atopic dermatitis (sometimes called eczema)
• Contact dermatitis (an allergic rash resulting from direct contact with a particular substance)
• Hives - a common type of itching rash that can be caused by a variety of skin or systemic conditions or drugs and chemicals.
• Fungal skin infections
• Insect bites and parasitic skin infections, such as scabies, can cause intense itching.

Systemic disorders

Systemic causes are less common than skin disorders but are more likely if there is no visible skin problem.

Some of the more common systemic causes are:

• Allergic reactions—for example, to foods, drugs, bites, or stings—that affect the body all over (called systemic allergic reactions)
• Disorders of the gallbladder or liver, such as gallstones, particularly when they cause jaundice
• Chronic kidney disease
• Less common systemic causes include hyperthyroidism (an overactive thyroid gland), hypothyroidism (an underactive thyroid gland), diabetes, iron deficiency, dermatitis herpetiformis, and polycythemia vera (a cancerous overproduction of red blood cells).
• Some disorders that affect the nervous system, such as multiple sclerosis, may cause itching. Some people who have mental 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 may 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

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.
 

Warning signs

The following symptoms may indicate that the cause could be more serious (not common):

• Weight loss, fatigue, or night sweats—may indicate a serious infection or a possible tumour
• 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 with any of the other warning signs or with severe itching should consult a doctor at their earliest convenience.

What the doctor does

Doctors ask many questions and look at the skin. 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.

Some Causes and Features of Itching

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

Contact dermatitis

• 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 a chemical substance including plants such as poison ivy)

Dry skin

• 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

Fungal skin infections

• Includes as ringworm, jock itch, or athlete's foot
• A circular rash with raised borders, scaling, and often hair loss
• In adults, usually on the feet or genital area
• In children, usually on the scalp or body

Hives (urticaria)

• Red, raised swellings that have sharp borders and are often pale in the centre
• Hives go away within hours, but new hives continue to appear, sometimes for days to months

Insect bites

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

Lichen simplex chronicus

• Areas where repeatedly scratched skin has thickened
• Areas are red, scaly, raised, rough, and separated from surrounding skin

Psoriasis

• Raised red patches with silver scales
• Usually on the outer exposed surface of the elbows or knees or on the scalp or trunk

Scabies

• 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)

Systemic causes

Note: This list is alphabetical and not according to probability. The causes listed here are usually rare.

Allergic reactions that have internal effects

• Widespread itching
• Often a raised red rash and sometimes hives

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

Chronic kidney disease (advanced)

• Widespread itching and no rash
• Sometimes worse during dialysis and sometimes worse on the back

Diabetes

• Frequent urination, thirst, and weight loss
• Itching usually occurring only after other symptoms have developed

Drugs

• Examples are aspirin, barbiturates, cocaine, morphine, penicillin, and some antifungal and chemotherapy drugs
• Sometimes no rash

Gallbladder or liver disorders

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

Iron deficiency anaemia

• Tendency to tire easily
• Sometimes paleness, weakness, headache, hair thinning, pica (craving non-foods such as ice, dirt, or pure starch), or difficulty breathing

Multiple sclerosis

• Intense itching that comes and goes
• Other symptoms of multiple sclerosis, such as numbness and tingling, weakness, loss of vision, vertigo, and clumsiness

Pregnancy

• Usually widespread itching without rash, developing sometimes in late pregnancy (called cholestasis of pregnancy)
• Sometimes resulting from mild liver problems

Psychologic factors

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

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

Tests and special investigations

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 analysed.

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 skin prick 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

Divided into the following groups:

• Skin care
• Topical treatments
• Systemic treatments
• Disorders that cause itching are treated. Sometimes other measures can also help relieve itching.

Skin care

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 moisturizers can also help, as can humidifying dry air (for example, in winter) and not wearing tight or wool clothing.

Topical treatments

Topical treatments involve substances that are applied to the skin. Topical treatments are used only if a specific area is affected. Options include lotions or creams that contain menthol and/or camphor, pramoxine, capsaicin, or corticosteroids. 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 odours but can be soothing, 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 atopic dermatitis, contact dermatitis, psoriasis, and lichen simplex chronicus.

Corticosteroids should usually not be used when:

• The skin is infected.
• An infestation is present.
• No rash or skin abnormalities are present.
• The cause is systemic.

Creams and lotions that contain the antihistamine diphenhydramine or the anaesthetic benzocaine usually should not be used because they can sensitize the skin and cause more itching.

Exposure to ultraviolet light at a doctor's office or in the home (phototherapy) may help relieve itching when other treatments are unsuccessful.

Systemic treatments

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 older 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.

KEY POINTS

• Itching usually results from dry skin, a skin disorder, or an allergic reaction.
• If the person has no rash or skin abnormalities, the cause may be a drug, an allergic reaction that has internal effects, or a systemic disorder.
• Skin care measures (such as limiting bathing, moisturizing the skin, and humidifying the air) can usually help relieve itching.
• Itching can usually be relieved by topical or systemic treatments.

About the author

Dr Mercedes E. Gonzalez

MD

Clinical Assistant Professor of Dermatology, University of Miami Miller School of Medicine; Clinical Assistant Professor of Dermatology, Florida International University Herbert Wertheim College of Medicine; Medical Director, Paediatric Dermatology of Miami

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