What exactly is a cold sore?
A cold sore, often called fever blisters or herpes labialis, is a frequent viral condition caused by the herpes simplex virus (HSV). After the virus first enters the body, it hides in an inactive state within the nerve endings beneath the skin, only to reactivate later as a cold sore. Many people first sense a tingling or itching feeling around the lips or mouth, which soon becomes painful, fluid-filled blisters that dry out and form a crusty layer. These outbreaks usually clear up in 10 to 14 days and are particularly contagious, especially in the early days of the outbreak. Cold sores affect a large portion of the population, with about 3 out of 4 Australians carrying herpes simplex virus type 1 (HSV-1), the leading cause of cold sores. Many remain unaware they are infected, as the virus often stays dormant with no visible symptoms. It is most commonly contracted in childhood or early adulthood, and once infected, the virus stays in the body for life. While there’s no permanent cure, various treatments can help ease symptoms and reduce the chances of future flare-ups.
What leads to cold sores?
Cold sores occur when HSV enters through tiny abrasions in the skin or the delicate mucous membranes of the mouth, genitals, anus, or urethra. Transmission happens through direct contact with an infected person. After infection, the virus becomes inactive in the nerve cells under the skin. While some people may never notice any symptoms, others, about one-third of those infected, may experience recurring outbreaks. These are usually triggered by factors like emotional stress, illness, or extreme weather, resulting in the signature tingling and eventual blisters. This isn’t a new infection, but a reactivation of an earlier one.
HSV-1 vs HSV-2: What's the distinction?
Cold sores are part of the herpes virus group, which includes oral herpes, genital herpes, and shingles. The herpes simplex virus has two main types: HSV-1 and HSV-2. Most cold sores that appear near the mouth, nose, or chin (commonly called oral herpes) are caused by HSV-1, whereas HSV-2 is more often linked to genital herpes. However, both virus types can affect either area, depending on the nature of the skin-to-skin contact. Estimates show that 75% of Australians have HSV-1, and around 12% carry HSV-2. Even though many people are infected at some point in life, not everyone will develop sores, since the virus often stays dormant unless reactivated by a trigger.
How are cold sores transmitted?
Cold sores are highly contagious. They are often spread by kissing someone who has an active sore or is about to develop one, during which the virus is “shed” from the skin. You can also catch it through contact with the fluid from a blister. Transmission can even occur without visible symptoms, a process called asymptomatic shedding, where the virus is still present on the skin. Because both HSV-1 and HSV-2 can lead to cold sores, the virus can be passed through more than just kissing. Common modes of transmission include:
- Using shared items like cutlery, razors, towels, or drinks
- Direct skin contact during sex or oral sex
- Sharing intimate objects
- Engaging in sexual activity, even with protection, if the virus is active outside the protected area
- Kissing or touching the face of someone with a cold sore
Typically, symptoms from the initial infection may not show up right away. The virus may linger silently until something causes it to reactivate. Once it does, cold sores usually appear in the same location as before. If you develop a cold sore, the original exposure may have occurred months or even years earlier, often without your awareness.
Recognizing the Symptoms and Phases of Cold Sores
Although cold sores are bothersome, their development usually follows a consistent pattern and tends to resolve within 2–3 weeks without leaving behind any permanent marks. The intensity and frequency of cold sore outbreaks differ from person to person. Most cases progress through a series of defined phases 3,4: In addition to the appearance of blisters, individuals may also experience a variety of accompanying symptoms, such as:
- Raised temperature
- Fatigue
- Upset stomach
- Enlarged lymph nodes
- Head pain
- Swollen or painful mouth area
- Irritated throat
- Risk of dehydration
What Causes Cold Sores to Flare Up?
The herpes simplex virus (HSV) can remain dormant within your nerve pathways. For some individuals, external factors like catching a cold may trigger a reactivation of the virus, hence the term “cold sore.” Some people encounter just a couple of episodes during their lifetime, while others may face recurring outbreaks. That’s why learning what sets off your cold sores and how to manage those triggers is essential. Common activators include:
- Emotional stress or psychological distress
- Other viral illnesses (e.g. flu or respiratory infections)
- Physical exhaustion
- Exposure to UV rays
- Windburn or cold weather
- Changes in immune function
- Skin trauma
- Alcohol consumption
- Menstruation
Options for Managing Cold Sores
While there’s currently no permanent cure, using antiviral treatments early on can help reduce both the severity and length of symptoms. Acting quickly may also help prevent complications and reduce the chances of the virus returning. You can ease symptoms through the following measures:
- Antiviral agents, Both oral tablets (like Famciclovir) and topical options (such as Aciclovir) are available over-the-counter and should be used at the earliest sign of a sore. These help to inhibit the virus from multiplying and may shorten the duration of the outbreak.
- Prescription-strength tablets may be advised in certain cases
- For people with frequent episodes, daily preventive treatment may be suggested by a doctor or pharmacist
- Povidone-iodine products (e.g. Betadine) may help by offering local antiviral protection
- Applying ice packs or cool compresses may ease discomfort
- Pain relievers like paracetamol can help reduce pain
- Moisturizing lip balms (e.g. petroleum jelly) can soothe dry or cracked lips, especially helpful during the crusting phase
- Cold sore patches (e.g. Compeed) protect the sore and support healing while limiting viral spread
- Keep the area clean and dry
- Avoid licking, touching, or picking at the sore
- If located around the mouth, consume soft foods
- Supplements like Lysine may offer preventative support
Minimizing the Spread of the Herpes Virus (HSV)
Cold sores can be easily transmitted, so these practices may help prevent passing the infection to others:
- Wash your hands after touching the affected spot
- Don’t touch your eyes or face after contact with a cold sore
- Don’t share items like towels, lip products, cutlery, toothbrushes, or cups
- Refrain from kissing infants and small children
- Avoid kissing or physical intimacy until at least 10 days after symptoms subside
- Stay away from individuals with compromised immune systems, eczema, or burns, as they are at greater risk of serious infection
Preventing Future Cold Sore Episodes
While there’s no absolute way to stop cold sores from happening, taking the following actions may reduce how often they occur:
- Identify and avoid known triggers
- Use lip balm with SPF when outdoors and protect against harsh weather
- Manage emotional stress
- Strengthen your immune system by maintaining good health
- Follow a nutritious diet
- Consume alcohol in moderation
When to Consult a Doctor
See your GP if your immune system is weakened, if symptoms are especially painful, if the cold sore has spread to other areas (especially the eyes), or if outbreaks are happening frequently. If you’re uncertain whether it’s a cold sore, a medical test can confirm the diagnosis and rule out other issues. If a cold sore becomes infected, antibiotics may be needed.