Understanding Itchy Skin or Pruritus

Localized and Generalized Causes of Itchy Skin

Hand feeling rash on arm
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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.

The Basics of Itching

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

In general, pruritus can be related to a problem with the skin or another underlying disease of the body (systemic disease). When itching is localized to a particular area of skin, it is usually caused by a local skin condition. Generalized itching, however, is related to systemic (whole body) causes roughly half the time.

The Scratch-Itch Cycle

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 cause.

Localized Pruritus Causes by Region

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. Let's look at these by location:

Various regions of the body: Skin conditions which may cause itching in many body regions include atopic dermatitis (eczema), contact dermatitis (skin inflammation related to contact with irritating substances), psoriasis, and scabies infection,

Scalp: Common causes of itching of the scalp include psoriasis, head lice, and seborrheic dermatitis (dandruff).

Eyelids: Common causes of eyelid itching include the causes listed above and allergic conjunctivitis.

Nose: The most common cause of nasal itching is allergic rhinitis (hayfever).

Ears: Itching of the ear canal has been associated with the causes above and otitis externa (swimmer's ear).

Chest, Abdomen, or Back: Common causes of itching of the skin on the main part of the body may include the conditions above as well as folliculitis, which is an inflammation of the hair follicles, usually due to a local infection.

Arms: Itching of the arms, especially the area at the bend of the elbow, is often due to psoriasis or atopic dermatitis. Other causes include xerosis (dry skin) and brachioradialis pruritis, which is itching along the upper arms, neck and shoulder blades related to sun exposure and nerve damage of the upper spine.

Legs: Itching of the legs is caused by many of the same diseases that cause itching of the arms, and atopic dermatitis is a very common cause of itching behind the knees. Pruritic rashes of the knees (and elbows) is commonly caused by psoriasis and dermatitis herpetiformis (the rash that often goes along with gluten sensitivity).

Hands and Feet: Itching of the hands and feet may be due to contact dermatitis, atopic dermatitis, pompholyx (dyshidrotic eczema), tinea (ringworm), and scabies.

Groin or Armpits: Common causes of itching of the groin and armpits include tinea (jock itch), contact dermatitis, scabies, and yeast infections.

Anus: Pruritus ani is the term used to describe itching in the anal regions. Pinworms are a fairly common cause of this condition, especially in young children. There are many other causes, including hemorrhoids, as well as  systemic medical conditions which will be discussed next.

Generalized Pruritus Causes

While generalized itching can be caused by skin conditions (such as scabies), a systemic condition is the cause in about 50 percent of people. Some of the conditions and causes of generalized itching, especially when a rash is not present, include:

Parasitic infections: Worldwide, infections with parasites (such as several types of worms) are a common cause of generalized itching

Medications: There are many medications which can lead to itching, either alone or a result of their actions on the liver. Medications which commonly cause itching without a rash include opiates (such as morphine or codeine) and medications used to prevent or treat malaria. Some of the newer targeted drugs used for cancer may cause itching with or without a rash. Many drugs can affect the liver and cause itching as a result of liver dysfunction.

Liver disease: Many types of liver disease, as well as liver dysfunction related to medications, can lead to itching without a rash

Iron deficiency: The skin is affected during iron deficiency anemia, It may be dry and develop hives or a rash.

Neuropathic itching: This type of itching is related to degeneration or entrapment of nerve fibers. Neruological causes of itching are often extremely frustrating as they do not respond to scratching and can be difficult to treat

Thyroid disease: Both hyperthyroidism and hypothyroidism can produce itching.

Kidney disease: Kidney disease commonly causes itching without a rash, and 25 to 50 percent of people on dialysis experience chronic itching.

Cancer: Leukemias and lymphomas may produce itching. Hodgkin's disease causes itching in 10 to 25 percent of people, though it's not certain why

Itching associated with hivesChronic urticaria (hives), especially dermatographism, and systemic forms of contact dermatitis are also common causes of generalized pruritus, even if no visible rash is present.

Diagnosing Generalized Pruritus

If you have generalized itching, your doctor will want to take a careful history and perform a physical exam. Tests for generalized pruritus, especially when no rash is present, may include a complete blood count, kidney function, liver function, thyroid function, iron level, stool studies for parasites, and a chest X-ray looking for evidence of lymphoma.

How is Itching Treated?

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 hence at least reduce the itch-scratch cycle. Non-specific treatments for itching may include topical steroid creams, oral antihistamines, and good skin care and moisturizing.

It is recommended that people with symptoms of itching, especially generalized pruritus, see their doctor for appropriate evaluation and treatment.

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