Cold Sores

What is a cold sore?

A cold sore (also called a fever blister) is a skin blister associated with a herpes simplex virus (HSV) infection. Cold sores typically form on your lips or the skin around your mouth. But they can also develop on other areas of your face, including your nose, cheeks or chin.

What are cold sore symptoms?

Cold sores themselves are a symptom of an oral herpes infection. This means the herpes simplex virus (HSV) entered your body at some point in your life and took up residence in your nerve cells. HSV stays dormant (latent, or “asleep”) in the nerves in your head and periodically reactivates, leading to cold sores.

The first time HSV infects you (primary infection), there may be other symptoms besides cold sores. These include:

• Fever.
• Sore throat.
• Redness and swelling in your throat.
• Painful sores inside your mouth, including on your gums, tongue and roof of your mouth (palate).

These symptoms may make it hard for you to eat or drink. Usually, you won’t have these symptoms later on when the virus reactivates. Instead, you’ll just have cold sores.

Possible complications in children

Primary oral herpes infections often happen during childhood, particularly in children between the ages of 1 and 5 years old. It’s important to watch for signs of dehydration if your child has trouble drinking enough fluids.

It’s also possible for your child to get another type of HSV infection on their fingers (herpetic whitlow) if they suck their thumb or touch their sores.

What are the cold sore stages?

Cold sores develop and go away over the course of one to two weeks. Here’s what you can expect for a typical cold sore outbreak:

• Day 1. You notice tingling, itching, pain or numbness on your lip or nearby skin. This is the area where cold sores will form. Healthcare providers call this the prodromal (pronounced “proh-DROH-mul”) stage. It means HSV has reactivated in your nerve cells and started making copies of itself (replicating). The prodromal stage is a warning sign that cold sores are about to form.
• Days 1 to 2. Within 24 hours of the start of the prodromal stage, bumps form on or around your lips (most often, along the outer edge). On average, three to five bumps form, but you could have more or fewer. Within hours, the bumps fill up with fluid and become blister-like. The area becomes red/discolored, swollen and painful.
• Days 2 to 3. The blisters break open (rupture) and ooze a clear or slightly yellow fluid. This is sometimes called the “weeping phase.”
• Days 3 to 4. The blisters stop oozing and a crust forms. The crust often looks like a golden-brown scab. It covers the sore as it heals but may sometimes crack open or bleed.
• By day 14. The scab usually falls off within six to 14 days of the start of the outbreak. The skin underneath may be a little more pink or red than usual for a few days before fully healing.

How long does a cold sore last?

Cold sores usually last one to two weeks. Symptoms may be more severe and sores may take longer to heal if you’re immunocompromised.

What causes cold sores?

A herpes simplex virus (HSV) infection causes cold sores. There are two types of HSV (HSV-1 and HSV-2). HSV-1 causes most cases of oral herpes, the infection that leads to cold sores. But HSV-2 can also cause oral herpes and related cold sores.

Many different things can trigger cold sores. Sickness, stress, sun exposure, trauma to your mouth area and hormonal changes (like during menstruation or pregnancy) are just a few examples. Knowing your triggers can help you avoid some outbreaks. But outbreaks can also happen unpredictably.

Are cold sores contagious?

Yes, they’re very contagious. Contact with someone else’s cold sore can cause you to develop an HSV infection. The location of the infection depends on which part of your body touches the cold sore.

For example:

• If you kiss someone who has a cold sore, you may develop an HSV infection in your mouth area (oral herpes).
• If someone who has a cold sore performs oral sex on you, you may develop an HSV infection in your genital area (genital herpes).
• If you touch a cold sore (on yourself or someone else) with your finger, you may develop an HSV infection on your finger (herpetic whitlow).

A person with a cold sore can spread HSV through skin-to-skin contact and also through their saliva. This means if someone you know has a cold sore, you should avoid:

• Kissing them.
• Sharing things that touch their mouth, including forks/spoons, straws, cups or lip balm.
• Touching their cold sore.
• Engaging in sexual activity that would involve contact with their cold sore.

How long are cold sores contagious?

Cold sores are contagious from when you first notice tingling or other skin symptoms (prodromal stage) until they completely heal. You’ll know the cold sore has healed when the scab falls off and the skin underneath looks back to normal.

Cold sores are most infectious within 24 hours of when they first form. “Infectious” refers to how much of a germ (in this case, HSV) you need to be exposed to in order to get sick. When a virus or other germ is highly infectious, it just takes a little bit to make you sick.

So, the first day you have a cold sore, it’s super easy for HSV to spread from the sore to someone else — for example, through kissing or sharing a straw. But HSV can still spread before and after that point, too, for the duration of the outbreak. This means as soon as you feel those warning signs that a sore might form, you should take precautions around others.

What should I know about cold sore treatment?

Treatment options for getting rid of cold sores include:

• Topical anesthetics. Topical anesthetics are gels you apply to the affected area. The medication numbs your skin to temporarily ease discomfort. This can make it easier for you to eat or drink.
• Topical antiviral medications. These are creams you apply to the affected area. You can get some without a prescription, like docosanol (Abreva® is a common brand name). Others, like penciclovir, require a prescription.
• Oral antiviral medications. These are medications you swallow. You need a prescription for them. Your provider may prescribe oral antivirals if it’s your first oral herpes outbreak or if you have severe outbreaks. Oral antivirals can also lower the risk of HSV complications (like ocular herpes and herpetic whitlow) in young children and people who are immunocompromised.

Topical anesthetics don’t affect healing. Antiviral medications help speed up the healing process. They’re most effective when started within 48 hours of the cold sore forming.

If you get frequent or severe cold sore outbreaks, your provider may recommend daily antiviral medications (chronic suppressive therapy). This form of treatment may help you have fewer and less severe cold sore outbreaks. Your provider can tell you more about what this involves and whether it’s right for you.

When should I call a healthcare provider?

Contact a healthcare provider about your cold sores if any of the following are true:

• It’s your first outbreak.
• You want to discuss treatment options. Antivirals are most effective when you take them as soon as you feel a cold sore coming on.
• The cold sore hasn’t started going away after about 10 days.
• You have sores that are very large or very painful.
• You’re not sure if you have a cold sore or something else.
• You have other symptoms like swollen gums or sores inside your mouth.
• You have atopic dermatitis or HIV (cold sores may be more severe or more likely to cause complications).
• You’re immunocompromised.

Call a pediatrician if your child develops a cold sore and any of the above scenarios apply.

Neonatal herpes

Newborns exposed to HSV won’t just get a cold sore — instead, they may develop a life-threatening condition called neonatal herpes. If you believe your newborn was exposed to HSV (for example, if an adult with a cold sore kissed them) or they have symptoms like skin blisters, call your pediatrician right away. Babies with neonatal herpes need immediate medical care.

Cold sore vs. canker sore — what’s the difference?

Cold sores and canker sores are both small, round sores that affect your mouth area. They have several important differences, including:

• What causes them. HSV causes cold sores, while canker sores have many causes that aren’t due to a virus.
• Whether or not they’re contagious. Cold sores are contagious. Canker sores aren’t.
• Exactly where they form. Cold sores usually form on your lips or around your mouth. Canker sores form inside your mouth.

Is it possible to have a cold sore inside my mouth?

Cold sores sometimes develop inside your mouth. This may happen when you first get infected with HSV. Later on, when the virus reactivates, you’ll likely only get cold sores on your lips and face. It’s different if you’re immunocompromised, though. In this case, you might get sores inside your mouth as part of oral herpes outbreaks.

Are cold sores always herpes?

Yes, cold sores are always a sign of a herpes simplex infection. But keep in mind that not every bump or irritation on your lip is a cold sore. For example, you might think you have a cold sore when really you have a pimple on your lip.

Talk to a healthcare provider if you’re not sure about any sores or blisters you notice. Your provider can help you determine if they’re cold sores or something else.