Another reason why you should avoid touching your cold sores, especially open ones, is to protect yourself. As with everybody, you have numerous bacteria on your fingers and under your fingernails. When your fingers come in to contact with an open cold sore, bacteria can enter into the sore and potentially cause infection. If cold sores resulting from a viral infection are secondarily infected by bacteria, you may have to deal with swelling, inflammation and pain in addition to the usual symptoms of a cold sore.
Moreover, when an open cold sore takes in bacteria and becomes infected, it can cause bleeding and lasting skin damage. This also comes with the risk of leaving a permanent scar near or on your lips.