HSV infections are mostly asymptomatic or unrecognised and can be spread, even if there are no Cold Sores/ blisters visible.
Some infections will cause blisters and sores ranging from mild to more severe.
Before Cold Sore lesions appear, they are often preceded by a sensation of pain, burning or numbness. Fluid filled blisters usually appear within 24 hours and weep until they scab over and heal. Episodes are usually mild and self limiting, settling on their own in 7-10 days.