While the triggers for an outbreak vary from person to person, the cold sore itself follows a relatively predictable course.
People who have frequent outbreaks are often familiar with this precursor symptom before the outbreak. There may not be any visible symptoms at this stage. You could however feel some tingling, burning or itching at this stage. It usually occurs in the first 24 hours of a cold sore and many treatments
are most effective when taken at this stage.
Virus replicate quickly in the first three days, and the cells react by causing inflammation to combat this. Blisters may begin to form in clumps and be sensitive to touch.
On the 4th or 5th day, the blisters may break open, creating a weeping ulcer. Fever may occur. This is often the most painful time during a cold sore outbreak, and the virus is extremely contagious at this stage.
A crust will form that may be yellow to brown in color. This may be unsightly but an important part of the healing process, and may last until 7 or 8 days in.
A scab forms as new skin begins to form underneath. Although the virus is retreating back to its latent stage, the area may still itch, and be irritating.