Cold sores are contagious for up to 15 days after you get the cold sore and most cold sores are contagious a few days before the cold sore actually appears.
So you may be contagious with the cold sore before you even get it.
Also kissing can trigger cold sores.
If you kiss someone who has a cold sore or is contagious with a cold sore virus known as the Herpes Simplex Virus then you can get the cold sore from the person who has a cold sore.
You should never kiss someone who has a cold sore until the cold sore has fully gone away.
Once your cold sore is gone then you can kiss as soon as the cold sore is gone.
You are no longer contagious with your cold sore when the cold sore has gone away fully.
A cold sore can remain contagious until the scabs and the cold sore has fully healed and disappeared.
So you should wait until after the scabs and the cold sore have completely went away and are no longer visible until you kiss someone.
Never kiss someone who has a cold sore and never kiss someone while you have your cold sore or you can easily spread your own cold sore to the person you kiss and they can spread the cold sore to you.
Cold sores are caused by a virus known as the Herpes Simplex Virus which is easily spread through kissing and other physical contact.
So just avoid kissing or coming into contact with the person until after the cold sores are gone fully.