Cold Sore Symptoms, Causes & Treatment Options

A cold sore is a skin lesion on the lips caused by infection with the herpes simplex virus (HSV). Cold sores are extremely common, harmless, and manifest as a visible red bump on the lip that is sometimes painful.

What Is a Cold Sore?

A cold sore is a skin lesion on the lips caused by infection with the herpes simplex virus (HSV). Cold sores are extremely common. In fact, most adults are infected with HSV, usually transmitted in childhood by normal close contact with parents, siblings or friends.

While the infection can be entirely unnoticed, or asymptomatic, the cold sores themselves are usually visible and sometimes painful. In an otherwise healthy individual, they are essentially harmless, though their appearance can cause a great deal of distress.

As with most viruses, there is no cure for HSV infection, though certain medications can decrease the rate of outbreaks for those who are severely afflicted.

You can safely stay home or try some minor treatments. As a viral infection, it will go away on its own without antibiotics. Balm mint cream (1%) or topical rhubarb-sage cream may improve symptoms, but it's not standard treatment.

Cold Sore Symptoms

With most adults infected by HSV, one might expect cold sores to be an extremely common sight. However, cold sores only appear during times of increased viral activity, commonly referred to as flares. In fact, it is not uncommon for an infected person to be asymptomatic.

When symptoms do appear, they are usually mild. The first cold sores may be seen within a few weeks of the original exposure, or not until the virus reactivates years later. Outbreaks at the time of primary infection can be more severe, involving painful mouth sores known as herpetic gingivostomatitis. Like other herpes sores, these fade after a few weeks and subsequent flares are usually less severe.

Main symptoms

The specific symptoms that do appear typically include the following.

  • Cold sores themselves: Cold sores are small, round lesions typically around the corners of the mouth. They often start as fluid-filled blisters on a red ("erythematous") base which then crust over once broken open. Most disappear within two weeks.
  • Burning, itching, or tingling: These are the classic symptoms associated with cold sores and can often arise several days before the lesions themselves.
  • Vague systemic symptoms: A low-grade fever can be seen at the time of first infection (several weeks before the appearance of cold sores).
  • Refusal to eat or drink: This may be a sign of oral herpes in young children.

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Causes of a Cold Sore

Cold sores are typically due to infections and higher risk activities and can flare due to certain factors.


Though there are many viruses within the herpes family, including those that cause chickenpox and mononucleosis, the two types which cause cold sores are herpes simplex virus 1 (HSV-1) and herpes simplex virus 2 (HSV-2). Historically, HSV-1 was thought to be the exclusive cause of oral herpes while HSV-2 was thought to only cause genital herpes. This pattern remains largely true, with the majority of cold sores still caused by HSV-1 rather than HSV-2. However, new research and changing sexual practices have led to an increased recognition that there is significant overlap between the two viruses and either one can cause oral or genital herpes.

As previously mentioned, infection with HSV is extremely common. Most people are carrying the virus before age 20. This makes it difficult to pin down the exact time and mechanism of exposure for the majority of people who develop cold sores. In most cases, it was probably something as simple as a kiss on the cheek between a mother and child. The virus can also be spread via inanimate objects exposed to bodily fluids, such as a shared drink or towel.

Higher risk activities

HSV is so widespread that complete avoidance is almost impossible. However, there are some higher risk activities.

  • Saliva exposure: Both HSV-1 and HSV-2 can be transferred via saliva, so sharing of drinks, lip balm, or other such items increases the risk.
  • Sexual contact: HSV-2 is generally transferred via sexual contact, making safe sex practices (using condoms) an important part of prevention. Unsurprisingly, a history of multiple sexual partners or sex with partners known to have HSV will increase the risk of infection.
  • Childbirth: It can also be passed from an infected mother to her baby during childbirth, though this risk can be significantly reduced with appropriate prenatal screening.


Once infected with HSV, the virus usually remains dormant in a person's system for many years. Specifically, cold sores are usually caused by reactivation of HSV-1 that has gone dormant in a nerve bundle known as the dorsal root ganglion of the trigeminal nerve. The exact cause of a flare is often unknown, but generally, it's a sign that the body's immune system is having trouble keeping the infection contained. As the outbreak progresses, the immune response is ramped up and drives the virus back into its dormant state.

Flares are usually triggered at times when the body is under physiologic strain by things like illness, hormonal changes, emotional stress or even a simple sunburn. Studies have found that flares tend to occur several times per year, with decreasing severity over time. That said, it is not uncommon for cold sores to occur once and never be seen again, just as it is not uncommon for someone infected with HSV to never notice a single cold sore.

Treatment Options and Prevention for Cold Sore

Supportive care

Supportive care is often all that is required for an otherwise healthy person since cold sores are not themselves dangerous. This can include:

  • Applying ice or a warm washcloth
  • Rinsing with salt water for mouth sores
  • Using analgesics such as acetaminophen (Tylenol)
  • Washing with soap and water: This is particularly important to prevent further spread.

Antiviral medications

Antiviral medications that are likely used for cold sores include the following.

  • Oral acyclovir: This is the mainstay of cold sore treatment. They have been shown to reduce the duration of pain, visible ulceration and viral shedding (which defines how contagious someone is). The related oral antivirals valacyclovir and famciclovir have also shown some efficacy, though there is less experience with their use.
  • Topical treatments: These do exist, including topical acyclovir, penciclovir, and docosanol. However, they are less effective than oral treatments and usually considered a second-line option.
  • Intravenous antivirals and hospitalization: These are never required for a routine cold sore in a healthy adult, but they are needed for newborns or severely ill people infected with HSV since they are at a higher risk of complications.


Prevention is difficult given the extremely high prevalence of HSV carriers, but there are things that can be done to decrease the chance of infection. The simplest step in prevention is avoiding contact with active herpes sores, including cold sores or genital herpes outbreaks. While transmission can occur in the absence of open sores, it is much less common. Nevertheless, it is always important to engage in safe sexual practices such as using condoms. It's also safer not to share drinks with strangers or anyone with open sores near their mouth.

When to Seek Further Consultation for a Cold Sore

Since cold sores are typically harmless, they usually do not require professional medical care. Most people don't even know they are infected, and there's no true cure once infection sets in. That said, there are times when an apparent cold sore merits seeing a physician. If you're concerned about an abnormal looking cold sore and want to make sure it's nothing more serious, most general practitioners or dermatologists should have no trouble clarifying.

If you are concerned about your appearance or experience frequent cold sores

On rare occasions, symptoms similar to oral herpes can be caused by other diseases that would require further testing to verify. Even if it is just a cold sore, those who are particularly bothered by their symptoms or have frequent outbreaks can speak to their physician about starting antiviral medications.

If you have other chronic or serious medical conditions or you are pregnant

Additionally, anyone with a chronic medical condition, particularly those that impair the immune system such as HIV/AIDS, should have a low threshold to check with a physician when concerned about new lesions. The same is true for women who are pregnant or thinking of becoming pregnant. While rare, the herpes simplex virus can spread to the central nervous system and cause far more serious damage. Thankfully this happens almost exclusively in those who are already severely ill with significantly impaired immune systems.

If you are concerned about spreading herpes

Lastly, anyone concerned about the sexual spread of herpes should be tested for other STDs since coinfection with multiple STDs is extremely common. While discussing these sort of intimate topics can be very difficult, it's important for your own safety and that of your partner(s) to be honest and open with your physician about any possible exposures.

Questions Your Doctor May Ask to Determine Cold Sore

  • Do you have a sore throat?
  • Which, if any, of these pictures match the gums or soft tissue in your mouth)?
  • Any fever today or during the last week?
  • Do you currently smoke?
  • When did you develop the sore/blister/bump?

Self-diagnose with our free if you answer yes on any of these questions.

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  5. Blevins JY. Primary herpetic gingivostomatitis in young children. Pediatr Nurs. 2003;29(3):199-202. PubMed Link