My husband and I are both sick with colds. He had a blister pop up on his upper lip today and I think it is a cold sore. Though, all the medical sites say he had to come in contact with another cold sore. This couldn't have happened because we have both been home in bed sick for a week. So my question is what caused this little blister? Was it the fever from being sick? If so why didn't I get one? Someone said he may have had them as a kid and just doesn't remember, help!