I used to be plagued for many years by cold sores on my lip. No longer!
Once you feel that familiar first tingling sensation, immediately grab a Q-tip, moisten it with water and then dip it in full-strength bleach. Squeeze the Q-tip so that it's just moist with the bleach solution. Then, place the Q-tip against the tingling area. Hold it there for about 3 minutes. Your cold sore won't develop!!
Why does this method work? Simple. Bleach kills EVERYTHING - including viruses. And, bleach is a gas. It penetrates through the surface of your skin and gets to the virus - NOW.
When you use this method ASAP upon feeling that first tingle, the virus will not have a chance to reproduce. It's the offspring of those first ones that do the real damage.
And, the good news is that the diluted bleach will not harm your skin tissue. At worst, you might simply have a very slight abrasion. But, I had no marks or ill effects whatsoever from this treatment. However, a tiny abrasion from the bleach solution is far, far better than the cold sore, don't you think?