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What Causes Cold Sores?

by | Jul 11, 2022 | Everyday Health

If you’re experiencing small blisters around the mouth, chances are you could have cold sores – also known as fever blisters. Caused by a strain of the herpes simplex virus, cold sores affect many adults in Australia.

During winter months, we commonly see an increase in the number of people affected by cold sores, with weakened immune systems or flu like symptoms often being followed by an outbreak of the virus.

What is a cold sore?


This viral infection is a form of herpes simplex and can be unknowingly spread from person to person, most commonly through skin to skin contact, like kissing or oral sex. As there is no cure and the virus is often dormant in the body, other ways that people get cold sores can be as simple as sharing eating utensils, drinking glasses, water bottles, or lip balm.

Herpes labialis, more commonly known as cold sores, are fluid-filled, small blisters around the mouth, often grouped together in small clusters. The average herpes simplex infection is asymptomatic, however when the virus is active in the body, symptoms of painful blisters and ulcers can be seen for up to 2 weeks.

The virus that causes cold sores is lifelong and the symptoms may recur over a number of years. It is important to note that a cold sore forms due to a viral infection. Unlike bacterial infections, which are treated with standard antibiotic drugs, viral infections require antiviral medication to be managed effectively.

Herpes simplex virus (HSV)

HSV-1 vs HSV-2

The herpes simplex virus type 1 (HSV-1) is often referred to as oral herpes and is vastly more common than genital herpes, which is referred to as herpes simplex virus type 2 (HSV-2). 

Although cold sores are a form of herpes, it is important to understand the difference between the strains of the herpes simplex virus and how differing symptoms present. Cold sores, also called fever blisters, are caused by the HSV-1 strain, while the HSV-2 strain is responsible for causing genital sores.

How common is the herpes virus?

Herpes infection may be more common than you think, with the World Health Organization (WHO) revealing an estimated 3.7 billion people under the age of 50 live with HSV-1, in a global study. In 2016, more than 178 million men reported living with the infection, worldwide. Meanwhile, in Australia, research suggests that approximately 75% of adults carry the HSV-1 virus.

When we break down these numbers, it’s easy to see that herpes is an incredibly common condition, not only globally, but right here in our backyard, too.

Symptoms of cold sores


As a mostly asymptomatic virus, oral herpes is generally quite a manageable condition and can be effectively treated, particularly when you are aware of the symptoms or warning signs leading up to a cold sore outbreak.

An active cold sore should last no longer than 2 weeks, with most people experiencing the physical affects for a much shorter time. Cold sores treated at the initial stages of development are likely to heal faster, with a noticeable reduction in pain from any formed blisters.

The first warning signs

A tingling sensation around the mouth is often the first warning sign that there may be an impending cold sore outbreak on the horizon. Most people experience an itching, tingling or burning feeling in the days leading up to the appearance of a cold sore.

In some cases, when experiencing your first outbreak, you may develop symptoms that mimic those frequently seen in other illnesses, including:

  • Sore throat

  • Headache

  • Fever

  • Muscle aches

  • Swollen lymph nodes

If you experience any of theses symptoms, seek medical advice, as a doctor can diagnose cold sores or rule out other health conditions, such as a flu, cold or other illness.

How cold sores develop

Severe mouth soreness is a common symptom once blisters form, as they can be present both in and around the mouth. When a cold sore appears, it is important to promptly commence your diagnosed treatment, in order to reduce symptoms.

Following this initial stage, the small blisters will break open, allowing the fluid inside to weep out, in preparation for the healing stage. While the blistering and weeping process can be quite sore, there are ways to alleviate the pain, including the use of a cool compress to reduce any burning sensations you may experience.

When the blister dries out, this is often referred to as the crusting stage, due to the current appearance of the cold sore. The final stage of development is where the healing begins. After the scabbed blister flakes away, the cold sore should heal completely, leaving no permanent damage.

What causes a cold sore outbreak?


Cold sores can be triggered by a variety of factors associated with physical health, psychological functioning and even weather conditions.

Stress and anxiety

Whether you’re working a high pressure job, have money concerns or are simply overdoing it in any aspect of life, all forms of stress and anxiety have the power to trigger an outbreak.

If you notice that cold sores return during high intensity situations, they’re likely caused by stress. Learning strategies to overcome anxiety will help you to minimise the chances of another outbreak the next time you’re facing a stressful situation.

Weather conditions

While harsh weather conditions are not the cause of cold sores, they certainly are one of the most common triggers. Sun exposure has been known to trigger cold sores, due to the presence of ultraviolet (UV) radiation. If you notice cold sores commonly forming after a day spent in the sun, protect your lips and reduce the chance of any small blisters forming, by using an SPF lip balm while outdoors.

In addition to hot sun, cold wind conditions have also been known to increase the likelihood of cold sores, as the lips become dried out and chapped. As with sun exposure, the best way to protect yourself from wind damage is to use a moisturising lip balm, to maintain skin hydration.

Weakened immune system

People are more likely to develop cold sores when they have a weakened immune system. Low immunity may be the result of a short-term health condition, such as influenza or a chest infection, but can also be caused by long-term health concerns, such as insomnia, nutritional deficiencies and autoimmune disease.

How are cold sores diagnosed?

Cold sores can be diagnosed in a number of ways, the most common being a visual assessment of the sores by your doctor. If the diagnosis is unclear, your doctor may take a sample by swabbing the skin cells, particularly if they suspect any further complications from the infection.


How can cold sores be prevented?

Promote healthy relationships and safe sex

Although HSV-1 causes cold sores and HSV-2 causes genital herpes, both strains of the herpes simplex virus can be contracted during close contact interactions, such as kissing or oral sex.

Having a cold sore can really cramp your style in the bedroom, especially when it comes to oral sex. The important thing to remember is that an open dialogue with your partner will allow you both to better understand the situation and what potential precautions should be taken, in order to reduce the risk of spreading the infection.

Be aware of what you’re sharing

The virus causing cold sores is easily spread, so when it comes to sharing, a little bit of vigilance goes a long way. Simply being aware of how oral herpes is spread allows you to make small changes to your lifestyle that will help to minimise the risk of infection.

Always use clean eating utensils, only wear lip balm that is your own and avoid sharing with others. These minor adjustments to your everyday habits will minimise the chance of spreading or contracting cold sores.

Cold sore treatments


As with any common health issue, there are a number of treatment options available for cold sore sufferers. If you’ve had a cold sore on more than one occasion, you’ve likely tried over the counter medicines, home remedies and prescribed medications.

Antiviral medications

Prescribed antiviral medicine has been clinically proven as one the most effective solutions for the early treatment of cold sores. When treated with oral antiviral medicine, patients reported a more noticeable improvement in the symptoms of cold sores, experiencing visibly clearer skin, when compared to those who only used over the counter treatments.

Administered orally, antiviral medication works by stopping the herpes virus from multiplying. These oral treatments are well tolerated by most people and can be used continuously to reduce the likelihood of recurrent cold sore outbreaks, or simply as needed when an outbreak occurs.

Let’s get your health sorted!



NIH National Library of Medicine. (2021) How effective are creams and tablets for the treatment of cold sores? (https://www.ncbi.nlm.nih.gov/books/NBK525789/)

World Health Organization. (2022) Herpes simplex virus. (https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus)

Disclaimer: The information provided in this blog is for general informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this blog. Reliance on any information provided in this blog is solely at your own risk. The health and medical information on this site is provided “as is” without any representations or warranties, express or implied.