Cold sores are contagious from the moment you first feel symptoms such as tingling, itching, or burning until the sore has completely healed and the scab has fallen off, which typically takes about two weeks (around 10 to 15 days)

. The stages of a cold sore and their contagiousness are as follows:

• Stage 1 (Day 1-2): Initial symptoms like tingling and itching; low contagion but still possible to spread the virus.
• Stage 2 (Day 2-4): Fluid-filled blisters form; moderate contagion.
• Stage 3 (Day 4-5): Blisters burst and ooze fluid; this is the most contagious stage.
• Stage 4 (Day 5-8): Sores dry out and scab over; contagion decreases but is still possible if the scab cracks.
• Stage 5 (Day 8-10+): Healing phase; low contagion until fully healed

Even after the cold sore has scabbed over, the virus can still be transmitted if the scab cracks and fluid leaks out. The herpes simplex virus type 1 (HSV-1) that causes cold sores can also be spread even when no visible sores are present, though this is less common than during an active outbreak

. To reduce the risk of spreading cold sores, avoid kissing, sharing utensils, or close contact while sores are present, and maintain good hygiene such as frequent hand washing

. In summary, cold sores remain contagious for the entire duration of the outbreak, roughly two weeks, from the first symptom until complete healing of the skin