Cold sores are usually caused by the herpes simplex virus (HSV) type 1.
HSV type 1 is really common and most adults who have it experience no symptoms and cannot ever remember having a cold sore, or never got one when the virus was passed to them.
HSV is transmitted by skin to skin contact. When someone has an actual cold sore the clear fluid has lots of virus in it and passes easily. At other times the virus will come to the surface from time to time but you will not feel any cold sore symptoms. During this time the virus can be passed to another person but the chance is reduced because there are fewer viruses on the skin.
To answer your question it is possible that the cold sores could have been passed to you recently from kissing someone who did not have any obvious cold sore symptoms. But it is also possible that you already had HSV type 1 and have just started to experience symptoms.
The only way to know for sure is to get the cold sore tested. What we do is take a test from the cold sore to see what type of HSV it is (It usually comes back as type 1). The next thing we do is take some blood to test for the HSV antibodies. It can take a couple of months for these antibodies to show up in the blood so if it is a new infection we will find that the swab test is positive for HSV but the blood test is negative.
Here is a link for additional information on HSV
http://healthnurse.wordpress.com/fa...nsmitted-infections-sti/herpes-simplex-virus/
HN
www.healthnurse.wordpress.com
www.stiresource.com
www.bccdc.ca
