5 doctors weighed in:

When is it too late to apply zovirax (acyclovir) to cold sore?

5 doctors weighed in
Dr. Gregory Mosolf
Pediatrics
4 doctors agree

In brief: Never

It still helps to apply the cream after 4 or 5 days just a lot less.
Better to use it at first sign of a cold sore. It may not help much but can't hurt. Oral medications work well if you start at 1st sign.

In brief: Never

It still helps to apply the cream after 4 or 5 days just a lot less.
Better to use it at first sign of a cold sore. It may not help much but can't hurt. Oral medications work well if you start at 1st sign.
Dr. Gregory Mosolf
Dr. Gregory Mosolf
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