Cold Sores: Causes, Symptoms, Treatments, HSV-1, and Light Therapy

In this article, we’ll give an overview of cold sores and their symptoms, triggers, and treatments.

Questions about cold sores? Check out this cold sore FAQs for answers.

What are cold sores?

Cold sores—also known as oral herpes, herpes labialis, and fever blisters—are tiny fluid-filled lesions that form in clusters on the lips and around the mouth. They are caused by the herpes simplex virus type 1 (HSV-1).

Who gets cold sores?

Cold sores are very common and anyone could experience them. More than half of the United States has been infected with the virus that causes cold sores (HSV-1), though many people never develop cold sores or have any symptoms. About 20% to 40% of people who have HSV-1 develop cold sore symptoms around their lips. [1,2]

People of all ages can become infected with the virus that causes cold sores, but the majority of people with HSV-1 are exposed to it during childhood. It is possible to develop a cold sore at any age, though the chance of having a cold sore outbreak decreases after the age of 35. A cold sore can develop multiple times a year or only once or twice in your lifetime. The frequency of a cold sore outbreak varies widely from person to person. [1,2]

What causes cold sores? Herpes Simplex Virus and Cold Sores

Cold sores are caused by the herpes simplex virus type 1 (HSV-1), which is common and highly contagious. HSV-1 spreads by saliva or close contact, often through kissing or sharing foods, drinks, or oral products like lip balm. Many people are exposed to HSV-1 over the course of their childhood, but symptoms are often mild, so not everyone is aware they have the virus. [1,2]

Once a person has been exposed to HSV-1, the virus remains dormant in nerve cells for the rest of their life. From time to time, it may be activated or “woken up,” which results in a cold sore outbreak. Some people experience outbreaks fairly regularly, while others may only have a few through their adulthood. Others with HSV-1 may never experience symptoms, and never know they have the virus. [1,2]

What triggers a cold sore? Why/When do cold sore outbreaks happen?

When HSV-1 is activated, it travels through the nerves to the lips, where a sore develops. Different people experience very different outbreak triggers. These are some of the more commonly reported reasons or triggers for cold sore outbreaks:

  • Stress or anxiety
  • Fatigue
  • Illness (cold, flu, fever)
  • Hormonal changes (like menstruation and pregnancy)
  • Exposure to extreme hot or cold temperatures
  • Sunburn
  • Dry, cracked lips


Symptoms of Cold Sores

Cold sore outbreaks usually begin with a tingling or itching feeling around the lips. Over the next 24 hours, the area becomes redder and swells as a painful sore develops. For several days, the cold sore may break and ooze yellowish fluid. Within 4-5 days, a cold sore usually scabs over and stops oozing fluid, though it may crack or bleed as it’s healing. The sore is typically healed and gone in 1-2 weeks. Usually, cold sore outbreaks and symptoms are worse the first time they happen. [1]

How Serious are Cold Sore Outbreaks?

For the majority of people with cold sores, outbreaks are an occasional annoyance that can be managed and overcome in a few weeks. However, cold sores can be a far more serious medical concern for certain populations. In young babies, immunocompromised people, and those with eczema, cold sores can cause serious infections.You should seek medical care for cold sores if you have eczema, HIV, cancer, or a compromised immune system. You should also consult a doctor if you’re experiencing frequent and painful outbreaks, or if your outbreaks aren’t healing within a few weeks. [1]

Identifying cold sores

Is it a cold sore? Or something else? Cold sores may be confused with other small ulcers and blemishes in and around the mouth, like canker sores, acne, and other blisters.

Cold sore or canker sore?

Cold sores appear on and around the lips. Canker sores only occur inside of the mouth, and they aren’t contagious or caused by the herpes simplex virus. If an ulcer is inside your mouth, it is not a cold sore.

Cold Sore or Pimple? Cold Sore or Acne?

Cold sores and pimples around the lips can look and feel very similar, but there are key differences. Cold sores usually appear in the same areas of the lip each time, while acne may appear anywhere on the face. Cold sores often appear in small clusters, while pimples and blackheads appear one at a time. Cold sores may hurt, but acne is more acutely painful to the touch and feels more pressure-filled.

Cold Sore or Chapped Lips?

Dry, cracking, and peeling lips are the hallmarks of chapped lips. A cluster of cold sores usually only occurs on one or two spots around the lips, while chapped lips tend to affect much of the lips at the same time, top and bottom. Cold sores are found on the edges of the lips, where chapped lips cause vertical cracks through the whole lip.

Treatments for Cold Sores

There is no cure for HSV-1 or cold sores, but people use ointments, medications, home remedies, and light therapy to lessen pain and manage outbreaks. Many people who experience cold sores let them heal on their own over the course of a week or two. In other cases, people use a range of natural and medical solutions to lessen the pain. Light therapy is also showing success limiting pain and speeding healing time in numerous peer-reviewed clinical studies, outlined below.

Creams and Ointments for Cold Sores

Antiviral ointments like penciclovir (Denavir) are sometimes used to control pain. Ointments work better the sooner they’re applied during a new outbreak, and typically need to be re-applied several times daily. Docosanol (Abreva) is a leading over-the-counter cream. [3]

Prescription drugs for cold sores

Some people choose to treat cold sores with oral antiviral drugs like acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex). Doctors may prescribe these medications if outbreaks are frequent and severe. Consult with a trusted physician. [3]

Home Remedies for Cold Sores (Natural and DIY treatments for cold sores)

People have reported anecdotal relief with hundreds of natural, at-home, and over-the-counter methods over the years. To ease pain, many people with cold sores apply ice or a wet washcloth, and use lip balm, Vaseline, or petroleum jelly. Lysine supplements and aloe vera are popular DIY solutions. Other methods include tea tree oil, essential oils, lemon extract or lemon balm, oregano, zinc, camphor, and witch hazel. Some people use honey, hydrogen peroxide, coconut oil, turmeric, apple cider vinegar, baking soda, Vitamin C, and Vitamin E. Keep in mind that these are non-medical options that haven’t been proven in clinical trials. Light therapy for cold sores has been tested and analyzed in peer-reviewed clinical trials. Below, we break down the published scientific research on light treatments and cold sores, or herpes labialis.

Light therapy for cold sores

Light treatments are used against cold sores and outbreaks to limit pain and improve healing outimes. Light therapy doesn’t come with the potential side effects of drugs, but unlike other at-home treatments, the science behind light treatments and cold sores is well-established in peer-reviewed studies.

One example of a home use light therapy device for cold sores is the Luminance RED Cold Sore Treatment Device.

Clinical research on light therapy and cold sores

Hundreds of clinical studies on light therapy and skin health have shown healing and pain relief benefits from specific wavelengths of light. Numerous clinical studies have been conducted specifically on light treatments and cold sores, with positive results for pain, healing outbreaks, and improving comfort and quality of life.

Light treatments also show great potential for preventing and limiting cold sore outbreaks as the begin. In 2018, researchers conducted a systematic review of all clinical trials that have been done on cold sores and light therapy. Every study they reviewed showed light therapy “to be effective in the management and prevention of recurrent herpes labialis, without any side effects.”  [4] Another comprehensive review of trials on cold sores and light therapy concluded:  “Phototherapy appears to strongly decrease pain and the interval of recurrences without causing any side effects.” [5]

The authors also noted that light therapy’s effectiveness against cold sores, and the lack of side effects and drug interactions with light therapy, was “especially helpful for older and immunocompromised patients.” [5]

Light therapy, cold sore outbreaks, and healing

Peer-reviewed trials around the world have demonstrated improved healing results for cold sores after light therapy treatments. The authors of a 2012 trial on cold sores and light therapy noted that “several pharmaceuticals are available to reduce symptoms and improve healing of cold sores, but only light therapy has been reported to significantly influence the length of the recurrence period.”

These researchers set out to test light therapy treatments against acyclovir, a leading cold sore drug option. The trial analyzed 232 patients with HSV-1 and cold sore outbreaks. Half of patients received light therapy treatments, while the other half received acyclovir. They were all monitored for a year to check on recurrence of their cold sores. The results of the trial showed “an obvious healing effect of light therapy” both initially and for the length of the year. Researchers demonstrated that light therapy was as effective as acyclovir, and concluded: “Light therapy of HSV-1 appears to be an effective treatment modality without any observed side effects.” [6]

Clinical research points to faster cold sore healing after light therapy

A 2013 randomized clinical trial analyzed 87 patients with recurrent cold sore outbreaks. Half of the patients received six light therapy treatments over the course of two days. Half of the patients received placebo treatments that looked the same. Analyzing the results, the researchers found that healing time in the light therapy group was significantly faster than the placebo group, with no side effects. [7]

A separate trial showed people using light therapy treatments healed an average of 3 days faster from a cold sore outbreak than people who weren’t treated. The study found that using a light therapy device around the mouth during an outbreak reduced healing time by over 3 days, from 9.4 days to 6.3 days.

Researchers reported that “the time the cold sore took to form a crust was also reduced” and concluded that there was a “significant difference between mean healing times,” showing light therapy is “an effective means of treating herpes labialis (cold sores).” [8]

Research Shows Potential Prevention of Cold Sores with Light Therapy

In a foundational study on light therapy and cold sores, 50 patients with recurrent outbreaks were monitored for a full year. Patients in the light group received daily treatments for two weeks, while patients in the placebo group received sham treatments. After a year, the results were dramatic:

  • Patients in the light therapy group averaged 38 weeks between outbreaks
  • Patients in the placebo group averaged only 3 weeks between outbreaks

That was after only two weeks of light treatments. The researchers wrote: “We demonstrated that a total of 10 irradiations with low-intensity laser therapy significantly lowers the incidence of local recurrence of herpes simplex infection.” [9]

Other trials and studies have shown that light therapy treatments can lead to long-lasting periods without cold sore symptoms. Case studies published in Brazil in 2011 demonstrated patients with recurrent cold sore outbreaks who “remained symptom free during the 17-month clinical follow-up period.” [10] Additional Brazilian case studies have shown that people with recurrent outbreaks “reported pain relief and did not show any signs or symptoms of recurrent cold sores” after a course of light therapy. The researchers added that “a favorable healing process was observed in all cases.” [11]

One study of a person with recurrent cold sores also found that “pain sensitivity was completely gone after the first treatment” with light therapy. [12]

Side Effects

Numerous reviews of the clinical research on light therapy and cold sores have found it to be effective for pain relief, healing, and also found light treatments to work “without causing any side effects.” [4,5]


Cold sores are tiny fluid-filled lesions that form in clusters on the lips and around the mouth. Caused by HSV-1, cold sores are very common and contagious. Clinical research is showing how light therapy can have a significant impact on the healing and potential prevention of cold sores. Crucially, numerous studies have shown that light therapy is well-tolerated for people with cold sores, with no reported side effects across a wide range of clinical studies.

As light therapy becomes more widely adopted for the treatment of skin conditions, it will be important to conduct more clinical trials to better standardize treatment parameters for specific conditions like cold sores. [5]

Sources and References:

[1]  Cleveland Clinic. Cold Sores.

[2]  WebMD. Cold Sores.

[3]  Healthline. Cold Sores.

[4] Al-Maweri SA, Kalakonda B, AlAizari NA, Al-Soneidar WA, Ashraf S, Abdulrab S, Al-Mawri ES. Efficacy of low-level laser therapy in management of recurrent herpes labialis: a systematic review. Lasers Med Sci. 2018 Sep;33(7):1423-1430.

[5] de Paula Eduardo C, Aranha AC, Simões A, Bello-Silva MS, Ramalho KM, Esteves-Oliveira M, de Freitas PM, Marotti J, Tunér J. Laser treatment of recurrent herpes labialis: a literature review. Lasers Med Sci. 2014 Jul;29(4):1517-29.

[6] Muñoz Sanchez PJ, Capote Femenías JL, Díaz Tejeda A, Turner J. The effect of 670-nm low laser therapy on herpes simplex type 1. Photomed Laser Surg. 2012 Jan;30(1):37-40.

[7] Dougal G, Lee SY. Evaluation of the efficacy of low-level light therapy using 1072 nm infrared light for the treatment of herpes simplex labialis. Clin Exp Dermatol. 2013 Oct;38(7):713-8.

[8] Hargate G. A randomised double-blind study comparing the effect of 1072-nm light against placebo for the treatment of herpes labialis. Clin Exp Dermatol. 2006 Sep;31(5):638-41.

[9] Schindl A, Neumann R. Low-intensity laser therapy is an effective treatment for recurrent herpes simplex infection. Results from a randomized double-blind placebo-controlled study. J Invest Dermatol. 1999 Aug;113(2):221-3.

[10] Ferreira DC, Reis HL, Cavalcante FS, Santos KR, Passos MR. Recurrent herpes simplex infections: laser therapy as a potential tool for long-term successful treatment. Rev Soc Bras Med Trop. 2011 May-Jun;44(3):397-9.

[11] Marotti J, Sperandio FF, Fregnani ER, Aranha AC, de Freitas PM, Eduardo Cde P. High-intensity laser and photodynamic therapy as a treatment for recurrent herpes labialis. Photomed Laser Surg. 2010 Jun;28(3):439-44.

[12] Bello-Silva MS, de Freitas PM, Aranha AC, Lage-Marques JL, Simões A, de Paula Eduardo C. Low- and high-intensity lasers in the treatment of herpes simplex virus 1 infection. Photomed Laser Surg. 2010 Feb;28(1):135-9.

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