What Causes Cold Sores?

Cold sores, also known as oral herpes or herpes labialis, are when small, usually painful, fluid-filled blisters develop around the corners of your mouth, lips, and sometimes gums. Herpes simplex viruses cause this condition. Let's review what causes cold sores, how to prevent them, and if they are contagious. We'll also discuss the symptoms and treatment below.

What Is the Primary Cause of Cold Sores?

There are two types of herpes simplex viruses, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). Typically, HSV-1 causes cold sores, but HSV-2 can also cause them. They can be spread through bodily fluids when kissing, having oral sex, or sharing everyday items, such as eating utensils.

Herpes simplex virus affects the face's nerve cells (also called ganglia). When affected or the virus becomes activated, the virus moves along the nerves of the lips and mouth causing a cold sore. Cold sores are also sometimes called fever blisters. HSV-1 and HSV-2 are chronic infections, meaning that once you are infected, you'll always have the virus.

How Can I Prevent Cold Sores?

Cold sores can spread through contact with another person that has the virus or by exchanging bodily fluids. Below are a few risk factors and prevention steps:

  • Do not kiss anyone when they have active cold sores
  • Do not share towels, dishes, or eating utensils with others
  • Avoid oral sex, especially if someone has active cold sores
  • Wash your hands after touching your face, mouth, or lips

If you have a history of cold sores, several things can activate the herpes virus and cause cold sores to appear. By avoiding these, you can potentially prevent cold sores from appearing. Try to avoid the following:

  • Temperature extremes, such as very hot or cold
  • UV rays, like those in a tanning bed
  • Chapped or cracked lips
  • Increased stress

Are Cold Sores Contagious?

Yes, cold sores are contagious. As mentioned above, you can get them through contact with another person that has the virus. This transmission can occur through physical contact, such as touching the cold sores, or through oral contact, like saliva. You are more likely to contract cold sores if the person has an active infection (meaning you can see them). However, since it's a virus that causes cold sores, you can still get it when the person doesn't have symptoms of an active infection.

What Are the Symptoms of a Cold Sore?

Often, people with HSV-1 do not ever have symptoms, also called asymptomatic. If you've never had a cold sore before, people will often experience early symptoms before cold sores ever appear. These can include

  • Fevers,
  • Tender lymph nodes around the face and neck,
  • Feeling generally unwell,
  • Muscle aches,
  • And a tingling or burning sensation around the lips (usually, this area becomes a cold sore).

After about a week of these symptoms, cold sores will typically start to appear. They can be a single fluid-filled blister or multiple clusters of little blisters. After about two to six weeks, the blisters will begin to crust over, and symptoms will subside. The virus then remains inactive in your body until reactivated again.

If you've had cold sores before, your symptoms will often be the same as your first time. However, they are typically milder, and symptoms before cold sores appear will last about a day. If you think you have cold sores, seeing your doctor is essential.

Are There Any Treatments for Cold Sores?

Treatment will differ slightly depending on whether it's your first time experiencing a cold sore or recurrent. If it's your first time having cold sores, your healthcare provider will often prescribe an oral antiviral for seven to ten days. Antivirals help calm down the virus and shorten the time you experience symptoms. They may also recommend over-the-counter creams for cold sores to help with symptoms. For pain relief and inflammation, you can take over-the-counter medications, such as acetaminophen or ibuprofen.

If you have a recurrent infection, symptoms are usually milder than the first time. If you need an oral antiviral, your healthcare provider will give you a shorter course. Sometimes though, people find symptoms aren't as bad and can use over-the-counter medications to manage them.

Are There Any Potential Complications of Cold Sores?

Cold sores do not often cause complications; however, in some cases, they can lead to severe conditions:

  • Genital herpes: Cold sores, or HSV-1, can be spread through oral sex. This transmission can cause an HSV-1 genital herpes infection.
  • Encephalitis: If you have a weakened immune system or are receiving chemotherapy, you have a greater chance of developing encephalitis. Encephalitis is swelling of the brain, which is life-threatening.
  • Eczema Herpeticum: If you have eczema (also called atopic dermatitis), herpes viruses can potentially worsen your eczema symptoms. Having cold sores with eczema can cause this life-threatening condition, known as eczema herpeticum.

Cold sores are highly contagious, so following these instructions is essential to prevent spreading or contracting the virus. If you have any symptoms of cold sores, seeing a healthcare provider is necessary. Some cases of HSV-1 and HSV-2 can lead to severe complications. So keep your follow-up appointments and seek immediate attention from a healthcare provider if symptoms worsen.


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Amanda Marten


Amanda Marten MSN, FNP-C is a freelance nurse writer and a certified family nurse practitioner. With ten years of nursing experience, she has worked in a variety of specialties including urgent care, travel nursing, post-surgical, and intensive care. In her free time, she enjoys gardening, outdoor activities, and spending time with her friends and family.