Can you pass on colsore virus without having a coldsore?

We put this question to Cambridge University researcher Ed Hutchinson:

I'm afraid, unfortunately the answer is sometimes, yes you can. Cold sores belong to a family of viruses called herpes viruses. These don't just include the famous sort of herpes we've all heard of but a whole range of viruses. These viruses have a nasty trick of causing visible infection then hiding and coming back at various points in your life. It's called latency. If the cold sore's happening it's hiding in some nerves in the side of your head and they're coming back into you're mouth on a regular basis. Sometimes this is going to cause a visible cold sore and sometimes it's going to cause something you can't see but it's still going to be shedding infectious virus into your saliva. I'm afraid it's always a risk.