Understanding Pruritus

Pruritus refers to an unpleasant sensation that causes the need to scratch, commonly called itching by most people. Itching may be localized to a certain area of the body or can be all over or generalized. When there is a rash that goes along with the pruritus, the cause is often easily determined and treated. However, the most difficult cases of pruritus are those without an associated rash.

Itching occurs when nerve fibers in the skin send a message to the brain via nerves. Itching and pain are closely related sensations, in that the same nerves transmit both signals to the brain.

In addition to whatever causes an itch in the first place, scratching can often lead to even more itching. This is referred to as the scratch-itch cycle and becomes important in treating the itch no matter the underlying cause.

When itching occurs on only one part of the body, it is usually caused by a problem in the skin. The specific area of the body that itches may give a clue as to the cause of the itch. Causes of localized pruritus by body part include:

• Whole body: atopic dermatitis, contact dermatitis, psoriasis
• Scalp: psoriasis, head lice, seborrheic dermatitis
• Eyelids: allergic conjunctivitis, allergic dermatitis
• Nose: allergic rhinitis (hay fever)
• Ears: otitis externa (swimmer's ear).
• Trunk: psoriasis, atopic dermatitis, folliculitis, scabies
• Arms: psoriasis, atopic dermatitis, brachioradialis pruritis
• Legs: atopic dermatitis behind the knees, pruritic rashes of the knee, xerosis (dry skin), dermatitis herpetiformis
• Hands and feet: contact dermatitis, atopic dermatitis, pompholyx, ringworm, scabies
• Groin or armpits: tinea cruris (jock itch), yeast infections
• Anus: pruritus ani, pinworms, hemorrhoids

While generalized itching can be caused by skin conditions, systemic disease is the culprit in around 50 percent of cases. Some of the conditions and causes of generalized itching, especially when a rash is not present, include:

• Allergies (including anaphylaxis and systemic dermatitis)
• Medications (including drug-induced allergies or demyelination)
• Liver disease (typically later-stage disease)
• Iron deficiency
• Neuropathic itch (caused by nerve entrapment or degeneration) 
• Thyroid disease (both hyperthyroidism and hypothyroidism)
• Kidney disease (especially during dialysis)
• Cancer (including leukemias and lymphomas)
• Parasitic infections
• HIV (commonly experienced soon after infection)
• Pregnancy

If you develop generalized itching with or with a rash, your doctor will want to take a careful history and perform a physical exam.

Tests for generalized pruritus may include a complete blood count, kidney function tests, liver function tests, thyroid function test, a stool culture, and an HIV test.

The best treatment of pruritus is to fix the underlying cause of the itching, whether that is a skin condition or a systemic disease.

Until the underlying problem is corrected, treatment may be needed to control the itch and reduce the itch-scratch cycle. Non-specific treatments for itching include topical steroid creams, oral antihistamines, and good skin care.

If you have severe or persistent symptoms of itching, especially generalized pruritus, see your doctor for appropriate evaluation and treatment.