Medically reviewed by Kristin Hall, FNP
Written by Our Editorial Team
Last updated 7/26/2020
Cold sores are small blisters and sores that can develop on and around the lips. They’re known medically as “herpes labialis” and they’re an extremely common occurrence, with about 2.5 out of every 1,000 people experiencing at least one outbreak per year.
Like other forms of herpes sores, cold sores are caused by the HSV-1 or HSV-2 viruses. Most cases of cold sores are the result of HSV-1, which affects more than two thirds of people aged 49 or below.
Cold sores typically heal on their own, usually over the course of one to two weeks. Most people that develop cold sores will experience occasional relapses, as the virus that causes cold sores remains dormant in the body even when you don’t have any physical symptoms.
Like all forms of the herpes simplex virus, cold sores are highly contagious. If you kiss someone while you have one or more cold sores, there’s a significant risk of the virus other person being exposed to and infected by the virus.
In this guide, we’ll explain how cold sores can transmit HSV-1 (and less frequently, HSV-2) from one person to another. We’ll also explain when it’s safe to kiss someone, engage in oral sex, or have any other kind of oral contact after a cold sore.
Cold sores spread through contact with infected people. Since cold sores are so prevalent, most people are already infected with the HSV-1 virus that causes them. In fact, most data shows that around two thirds of all people aged from 14 to 49 are infected with the HSV-1 virus.
Most people are infected with HSV-1 without ever realizing, often through contact with a sexual partner or an innocent kiss from a relative that unintentionally transmits the virus.
Even if you already have HSV-1 (or, less frequently, HSV-2), you might not ever develop a cold sore. This is because only a small percentage of people infected with HSV-1 or HSV-2 develop physical symptoms such as oral herpes (cold sores) or genital herpes.
Still, it’s important to take precautions to prevent cold sores from spreading even if you’re fairly confident you or your partner already have HSV-1. Often, kissing someone with a cold sore can trigger an outbreak in another individual even if they’re already infected with the herpes virus.
Cold sores usually take one to two weeks to heal. During this healing period, they’ll go through a consistent process, starting as a small blister on the lip that develops into an open sore before it heals over. Cold sores typically do not leave permanent scars, unless they become infected.
In fact, the development and healing process for a cold sore can be divided into eight stages, all of which have the potential for the virus to shed and spread to other people:
The first stage is the latent period. In this stage, the herpes virus is dormant in the body and you, if you’re infected with the virus, won’t notice any symptoms. During this stage, your body may still be shedding the HSV-1 or HSV-2 virus even without symptoms.
The second stage is the prodromal stage. During this period, people often experience a tingling sensation on or around the lips and red skin in the affected area. This stage lasts for one to two days in most people.
The third stage is the inflammation stage. At this point, the herpes virus targets cells in the lips or mouth, beginning the process of creating a sore. This takes around one day, with swelling and discomfort in the affected area.
The fourth stage is the pre-sore stage. Over the course of one to two days, a small, hard blister will begin to develop on or around the lips. These blister are often painful and can make eating, chewing and moving the lips uncomfortable for the affected person.
The fifth stage is the open herpes lesion stage. During this period, the blister (or blisters, if you have multiple sores) will open into an exposed sore. Most cold sores remain open for one to two days, during which they are highly infectious.
The sixth stage is the crusting stage. At this point, the body’s immune system begins to actively heal the sore by developing a brown, immunoglobulin crust. It usually takes two to three days for the crust to develop into a scab.
The seventh stage is the healing stage. At this point, a scab has fully enveloped the sore and new skin is developing underneath. The scab will typically remain for up to five days, during which the cold sore is still infectious.
The eighth and final stage is the post-scab stage. At this point, the sore will have healed and the skin will be returning to normal. It’s still possible for some redness to linger in the affected area for two to three days.
While cold sores usually develop on or around the lips, they can also develop inside the mouth -- a form of herpes infection called herpetic stomatitis.
Cold sores are contagious at all stages of the development and healing process, meaning you shouldn’t kiss anyone, share eating utensils, have oral sex or engage in any other oral contact throughout the entire process of a cold sore developing and healing.
In general, it’s best to wait for three to four days after the cold sore scab disappears before you kiss someone or engage in oral sex. This is because the herpes virus can continue shedding in the late stages of a cold sore healing, even if there’s no viral fluid present.
The longer you wait after an outbreak, the lower your risk of transmitting cold sores to a partner or other person. As always, it’s best to be patient and wait for the outbreak to completely clear up before you put yourself in a situation where spreading the virus is possible.
Cold sores can be extremely annoying, especially if they get in the way of you being intimate with your partner. Unfortunately, they can also carry a social stigma, making meetings, lunch with friends and other normal situations embarrassing and stressful.
There are several highly effective medications on the market that you can use to speed up the healing process and treat cold sores when they flare up. Often, treating a cold sore in its early stages (the prodromal stage) can prevent it from fully developing.
Of these medications, the most widely used is valacyclovir. Our Valacyclovir 101 guide covers everything you need to know about using valacyclovir to treat cold sores, from the medication’s mechanism of action in the body to common dosage periods, side effects and more.