What causes severe itching in renal dialysis patients during and after treatment???

Well since they are cleaning out your blood I guess that might have something to do with it. I remember reading somewhere that even scientists dont know what causes itching and what the purpose of it is. I might be wrong though.

Itching is a common complaint among dialysis patients, although not all patients are troubled by it. While no one knows the exact cause(s), itching may be brought about by:

Dry skin
High Phosphorus Levels
Allergic Reactions
High Blood Levels of Parathyroid Hormone (PTH)
Among dialysis patients, itching is most often caused by dry skin. It occurs because the skin is not making enough oil to moisturize itself. It is important to keep the skin clean and moisturized. It may help to use a moisturizing soap when you bathe, to apply unscented body oil, and to use body lotions.

Another factor related to itching may be your diet. In your blood, phosphorus combines with calcium to form phosphorus-calcium products. Some of these phosphorus-calcium products are excreted through your skin and this may cause you to itch. The best way to avoid this is to keep your phosphorus level normal. Maintain your dialysis diet and take phosphorus binders with each meal or large snack as directed.

Allergic reactions to the dialyzer, blood tubing or medications may occur during the hemodialysis treatment. Keep a record of how you feel during your treatment. Maintaining such a log may help you to pinpoint the causes of your itching. Discuss how you feel with your doctor or nurse. There are medications available that may help you.

A blood test can tell if you have a high level of parathyroid hormone (PTH). PTH levels are often elevated in dialysis patients due mainly to a decreased calcium level and an increased phosphorus level. This condition stimulates the parathyroid gland to secrete excessive hormones. This can lead to bone disease. Symptoms may or may not occur. If symptoms appear, the bone disease may already be severe. The most common symptoms are bone pain, joint discomfort and itching. Treatment includes controlling calcium and phosphorus levels with phosphate binders and taking Vitamin D.

Please consult your physician who is monitoring your dialysis.
Itching can be caused by a myriad of factors. It is not possible to be certain without knowing about your other activities such as eating, bathing, uses of the various types of soaps, etc.
Trust your doctor and ask him.