The Phases of a Cold Sore.

Prodromal
The symptoms during this phase are tingling, itching, burning, tightness, swelling, or numbness under the skin where the lesion will form. During this phase, the skin appears normal. Sometimes fever, headache, and muscle pains will be present as well. 

Macule
Redness of the skin

Papule
Small raised bumps with inflammation form on the skin. There may be some throbbing.

Vesicle
A clear fluid-filled blister will form. 

Postule
The clear liquid becomes yellow and pus forms.

Crust
A yellowish crust forms on the affected area.

Scab
The area becomes reddish, dry and itchy.

Healing
The pain disappears and the scab falls off.

The duration of a cold sore is usually 7 to 10 days.