Itch is an irritation in the skin that elicits an urge to scratch. Itches are a common problem and can be localized (limited to one area of the body) or generalized (occurring all over the body or in several different areas). The medical term for itching is pruritus. Generalized itch, for obvious reasons, is more difficult to treat than localized itch. Itches can also occur with or without skin lesions (for example, bumps or blisters). An itch that is accompanied by visible skin abnormality usually should be evaluated by a physician and, in some cases, by a dermatologist since the problem is likely to be a condition that requires specialized medical treatment (for example, eczema, scabies, etc.). Itching can be caused by many conditions. Probably the most common cause of itch is psychological, that is, due to stress, anxiety, etc. Stress also can aggravate itch from other causes. Dry skin is another frequent cause of itch. Many people also report sunburn itch following prolonged exposure to UV radiation from the sun. Other causes include metabolic and endocrine disorders (for example, liver or kidney disease, hyperthyroidism), cancers (for example, lymphoma), reactions to drugs, and 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. Common infectious causes of itch include a fungal infection of the crotch (tinea cruris) commonly known as jock itch, as well as vaginal itching and/or anal itching from sexually transmitted diseases (STDs) or other types of 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. Most people who have itching, however, do not have a serious underlying condition.

Wow - great answer from XT. Just one thing. Itching is a prelude to hurting/pain. Sometimes it's the body's way of alerting you that something's wrong or about to happening ...

It gives our finger nails something to do.