The short answer is that its not. In general, its best to wait until after the scabs and sores completely disappear before you kiss someone or engage in oral sex. This is because the herpes virus can continue shedding in the late stages of a cold sore healing, even if theres no viral fluid present.

How soon can you get a cold sore after being exposed?

The first time you have a cold sore, symptoms may not start for up to 20 days after you were first exposed to the virus. The sores can last several days, and the blisters can take two to three weeks to heal completely.