Itch (cont.)

Depending upon the underlying cause, itching may be associated with other symptoms and signs. Most commonly, these associated findings include skin lesions such as rash, blisters, bumps, or redness of the affected area. Dryness of the skin is a common cause of itch. Itching of skin can lead to tears in the skin (excoriations) from scratching. Less commonly, generalized itching can be a sign of chronic medical conditions such as liver disease. In these situations, there may be no changes to the appearance of the skin.

Itching can be caused by many conditions. A common cause of itch is psychological, that is, due to stress, anxiety, etc. Stress also can aggravate itch from other causes. Dry skin (xerosis) is another frequent cause of itch. Many people also report sunburn itch following prolonged exposure to UV radiation from the sun. Other causes of generalized itching that may not produce a rash or specific skin changes include metabolic and endocrine disorders (for example, liver or kidney disease, hyperthyroidism), cancers (for example, lymphoma), reactions to drugs, and interruptions in bile flow (cholestasis), diseases of the blood (for example, polycythemia vera). Itching is common with allergic reactions. Itching can also result from insect stings and bites such as from mosquito or flea bites.

Infections and infestations of the skin are another cause of itch. Genital itching, which may accompany burning and pain, in men and women can occur as a result of genital infections such as sexually transmitted diseases (STDs). Vaginal itching is sometimes referred to as feminine itching, and sexually transmitted diseases can also cause anal itching. Other common infectious causes of itch include a fungal infection of the crotch (tinea cruris) commonly known as jock itch, psoriasis, and ringworm of the body (tinea corporis), as well as vaginal itching (sometimes referred to as feminine itching) and/or anal itching from sexually transmitted diseases (STDs) or other types of infections, such as vaginal yeast infections. Another type of parasitic infection resulting in itch is the so-called swimmer's itch. Swimmer's itch, also called cercarial dermatitis, is a skin rash caused by an allergic reaction to infection with certain parasites of birds and mammals that are released from infected snails in fresh and saltwater. Itch may also result from skin infestation by body lice, including head lice and pubic lice. Scabies is a highly contagious skin condition caused by an infestation by the itch mite Sarcoptes scabiei that is known to cause an intense itch that is particularly severe at night.

Itching can also result from conditions that affect the nerves, such as diabetes, shingles (herpes zoster), or multiple sclerosis. Irritation of the skin from contact with fabrics, cosmetics, or other substances can lead to itching that may be accompanied by rash. Reactions to drugs or medications can also result in widespread itching that may be accompanied by a rash or hives. Sometimes women report that they experience generalized itching during pregnancy or a worsening of the conditions that normally cause itching.

Most people who have itching, however, do not have a serious underlying condition.

Source: MedicineNet.com
http://www.medicinenet.com/itch/article.htm