Dry skin, internal diseases or nerve disorders can cause itching under the skin, according to Mayo Clinic. These causes of itching under the skin may have no outward signs of skin disturbance.
If no rash or red bumps are present, dry skin, or xerosis, may be the cause of itching, says Mayo Clinic. Causes of dry skin may be environmental, such as low humidity, excess heat or extreme cold. Air conditioning, heaters and excessive exposure to water from bathing or showering too frequently may also result in dry skin.
Internal diseases that may cause itching under the skin include liver disease, cancers, thyroid conditions, celiac disease, kidney failure, and anemia caused by iron deficiency, according to Mayo Clinic. When internal diseases are the cause of itching, the entire body is affected. No outward sign of itching may be present on the skin, excepting the areas that have been scratched.
Nerve disorders that may cause itching under the skin include multiple sclerosis, diabetes mellitus, shingles and pinched nerves, says Mayo Clinic. Some women experience itchy skin with no obvious outward cause during pregnancy. Itching is especially common on the arms, thighs, breasts and abdomen.
An evaluation by a doctor may be necessary to determine the cause of the itching, says the Merck Manual Home Health Handbook. If itching is accompanied by weight loss, fatigue, night sweats, numbness, tingling, abdominal pain or excessive thirst, it may indicate a serious condition.