The National Institute of Dental and Craniofacial Research estimates that 500,000 Americans experience their first cold sore every year. For most, the first episode is also the last. A smaller number---between 20 and 40 percent--suffer recurrent episodes. Cold sores follow five characteristic stages: prodrome, blistering, ulceration, crusting and scabbing. The cold sore heals during the last two stages.
In the 2008 edition of "Harrison's Principles of Internal Medicine," University of Washington professor of virology Lawrence Corey, MD, explains that the herpes simplex virus that causes cold sores is what doctors call a lytic virus, one that essentially takes over an infected cell and uses it to make new copies of itself. The newly copied viruses escape the cell by causing it to explode. Healing begins when the immune system, sometimes aided by antiviral drugs, gains control over the virus and stops it from infecting new cells. Healing ends when the body replaces all of the cells destroyed by the virus.
According to Corey, the appearance of crusts signals that healing has begun. A crust is a sandy, yellow-brown, loosely adherent coating that represents the dried exudate of the cold sore. As the crust falls off, it leaves behind a scab, which is a flat, flaky plug of dead skin cells. Cold sores heal from the outside in. The center is the last part to heal. The scab reflects this process; it becomes progressively smaller in diameter until it flakes away entirely, leaving new skin that may be pink or pale compared to the surrounding skin.
Healing usually begins about five days after the cold sore appears. The crusting and scabbing stages each last about three to four days. The total time from the first appearance of the cold sore to complete healing ranges from 10 to 14 days. For people who experience recurrent bouts of cold sores, the first episode usually takes the longest time to heal.
In the 2008 edition of "Fitzpatrick's Dermatology in General Medicine," National Institutes of Health researcher Stephen E. Straus, MD, explains that cold sores heal when they are kept clean and dry. Oils and bacteria from surrounding skin can delay healing and increase the risk of developing a bacterial infection on top of the viral infection. Although it may be tempting to pick or play with cold sore crusts and scabs, doing so increases the risk of scarring. The Academy of General Dentistry recommends applying an aloe-containing lip balm three times per day to keep delicate, healing skin adequately moisturized and otherwise leaving the lesions alone.
Corey says that although people become less contagious as cold sores start to heal, it's still possible to spread the infection. In fact, viral particles have been detected on skin that exhibits no symptoms at all. People with a healing cold sore should abstain from intimate activities such as kissing and oral sex until the cold sore resolves completely.