That won't stop him from itching (only scratching) and might make it worse, especially if it's warm.. Make sure he doesn't have bugs. and that he's not getting too much protein. and you can try some olive oil on his food.
as fidget said, get rid of the sweater
you might want to treat him with revolution if he has been scratching around his head and shoulders or if you see any parasities http://ratguide.com/health/integumentary_skin/ectoparasites.php amount given is based on the strength of the med and the rats weight
make sure he is getting low protien (ie a low protien rat block (14%v or 15% because they do not make them lower) and a variety of daily vegs, plus healthy treats like berries, a piece of fruit, cooked whole grains, a few organic pumpkin seeds etc
if he has scabs, or irritated skin, please post some pictutres