When I was young and naive, I always got fever blisters on my lips. My neighbor brought over some cream in a plain silver tube. It worked miracles on my lips and when I would run out, he would always have more. I never had any idea what it was or why the label was always missing, but as I said, I was young and naive.
Many years later, he told me that it was preparation H, but he didn't tell me earlier because he didn't think I would have put it on my lips. He was right.