My 21yr old son has had itching all over his body for past 4 weeks. no other symptoms. no rash. what could it be?

?Scabies,allergy?: The cause of generalized itching can be an elusive dx. It can reflect reaction to a body wash , soap or laundry detergent. There is a human mite called scabies that can cause a persistent low grade rash & chronic itching for months until eliminated.Have your son do a lifestyle audit & list any new body treatments. If none are found, have your dr go over the other possibilities.

Many things: Liver disease, kidney disease, certain immunologic diseases, an array of hematologic diseases, cancers, endocrine disorders, medication reactions, and allergic reactions can cause an itch without a rash. Your son should see his doctor to have this evaluated.