Merck Manual

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Some Causes and Features of Itching

Some Causes and Features of Itching

Cause

Common Features*

Tests†

Skin causes

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 Poison Ivy Poison ivy is an allergic contact dermatitis that causes a very itchy rash caused by exposure to the oil urushiol, which coats the leaves of poison ivy plants. An itchy, red rash and multiple... read more 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

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

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

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

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

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 Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more Hyperthyroidism (an overactive thyroid gland): Difficulty tolerating heat, sweating, weight loss, bulging eyes, shakiness (tremor), restlessness, and sometimes an enlarged thyroid gland (goiter)

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.