Normally Skin diseases are spread by scratching the affected areas. You are actually transferring the germs to other parts of your body that come in contact with your hand. So you need to be very careful. Try to keep the affected area clean. Also do not scratch it. Even if you do make sure you don't touch any other part of your body. Wash it thoroughly before you do anything else. Since this wouldnot be possible try avoiding scractching the affected area.
