What can trigger a cold sore?

Cold sore triggers can be different for each person. Here are some common triggers to watch out for: Having an illness, like a cold or the flu Being tired Dental procedures or injury to the mouth Emotional or physical stress Sunlight or ultraviolet lamps

What Does a Cold Sore Look Like? Here’s How to Diagnose One

Key takeaways:

Cold sores (fever blisters) are painful sores caused by the herpes simplex virus (HSV).
Cold sores start as a group of blisters usually in or around the lips. The blisters will open up and eventually crust over before healing.
A cold sore breakout will resolve on its own. But it can also be treated with over-the-counter or prescription medications to improve symptoms and shorten its duration.

Cold sores are painful sores that develop in or around the mouth. They’re caused by the herpes simplex virus (HSV). And they can be spread by person-to-person contact (like kissing) or contaminated objects (like utensils). Once someone develops a cold sore, the virus stays inside the body, and cold sores can develop again.

Cold sores go through different stages before healing. Here, we’ll review what a cold sore looks like at each stage (with pictures), so that you can identify them and start treatment early.

What a cold sore looks like (with pictures)

Cold sores (or fever blisters) are common on or around your lips. But they can also develop:

Inside your mouth
Around your nose
On your chin

Here are what different stages of cold sores look like in different skin tones.

Stage 1: Blisters

Before a cold sore develops, you may feel tingling, burning, or itching in the area. Then, small, painful, fluid-filled blisters form. They can be yellow or pink, and the surrounding skin is usually red, violet, or brown. The blisters usually develop in clusters or groups.

Grouped blisters on the upper lip.

Stage 2: Open blisters

In the next stage, blisters burst open. This leaves open sores that can ooze a yellow fluid.

Open sores caused by herpes.

Close-up of open sores from herpes on the cheek.

Open sores on the cheek caused by herpes.

Stage 3: Crusting

After a few days, the open sores form crusts and scabs before they start to dry out. Cold sores will completely heal about 1 to 2 weeks after they start.

A herpes sore starting to crust over.

A cold sore starting to scab over.

What causes cold sores?

Cold sores are caused by the herpes simplex virus (HSV). There are two types of HSV: type 1 (HSV-1) and type 2 (HSV-2). HSV-1 causes most cold sores, while HSV-2 is the main cause of genital herpes.

How are cold sores diagnosed?

Most healthcare professionals can diagnose a cold sore by what it looks like and your symptoms. In some situations, a sample from the sore can be sent to a lab to confirm the diagnosis.

How can you treat a cold sore at home?

Many over-the-counter (OTC) treatments can provide relief from cold sores. Here are some of the options:

Docosanol (Abreva) cream
Benzocaine (Orajel) and benzyl alcohol (Zilactin)
Lysine ointment
Zinc oxide and glycine cream
Camphor and phenol (Campho-Phenique)
Herpecin L (dimethicone / meradimate / octinoxate / octisalate / oxybenzone)

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For most people, cold sores can be managed at home with OTC treatments. But sometimes prescription-strength pills (like acyclovir) are needed (more on this below).

When should you see a doctor about cold sores?

Some people with cold sores may benefit from seeking medical care. This includes people who:

Have cold sores 6 or more times a year
Have a weakened immune system
Get a cold sore near an eye
Have a cold sore that lasts longer than 2 weeks or that’s very painful
Have eczema

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Can cold sores be prevented?

Once you’ve had a cold sore, there’s a chance that it could come back. You can’t completely prevent a cold sore from reappearing. But here are some steps you can take to make it less likely:

Regularly use a lip balm with SPF protection
Throw away lip items that touched your cold sore
Lower stress
Keep your lips moist
Know and avoid your triggers

What can be mistaken for a cold sore?

Cold sores can sometimes be mistaken for other types of sores on or around the lips. These include:

If you’re not sure whether you have a cold sore or something else, a healthcare professional can help you figure it out.

Frequently asked questions

Cold sore triggers can be different for each person. Here are some common triggers to watch out for:

Having an illness, like a cold or the flu
Being tired
Dental procedures or injury to the mouth
Emotional or physical stress
Sunlight or ultraviolet lamps

No. A cold sore isn’t a sexually transmitted infection or disease (STI or STD). Most people get cold sores when they’re young through non-sexual contact (like coming into contact with saliva).

The fastest way to heal a cold sore is to start a medication (like Abreva cream or acyclovir pills) as soon as you feel the first symptoms. This can make the cold sores go away about a day faster.

The bottom line

Cold sores are common painful sores that develop in or around the mouth. They’re caused by the HSV and can be spread by direct contact or contaminated objects. Cold sores usually go through three stages before healing. They start as a group of blisters, which burst open into sores before crusting and forming a scab. Cold sores go away on their own, but using OTC or prescription medications can help them heal faster.

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Written by:

Maria Robinson, MD, MBA

Maria Robinson, MD, MBA, is a board-certified dermatologist and dermatopathologist who has practiced dermatology and dermatopathology for over 10 years across private practice, academic, and telehealth settings. She is a fellow of the American Academy of Dermatology and the American Society of Dermatopathology.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

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Images used with permission from VisualDx (www.visualdx.com).

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