What you need to know about sun exposure and cold sores

Many of us may have spent hours in the sun during the holidays and while the importance of using sunblock is well recognised, do you know that exposure to the sun and even wind can trigger the development of cold sores or fever blisters 1?

Fever blisters or cold sores are tiny, fluid-filled blisters that form on and around the lips and are often grouped together in patches 1. Despite their name, they are not caused by the common cold 2. Cold sores are caused by the Herpes simplex virus type 1 (HSV 1) and can spread from person to person by close contact such as kissing 1. Cold sores are most contagious when oozing blisters are present, but the virus can be transmitted to others even if a person has no visible blisters 1.

Approximately 90 percent of adults worldwide test positive for evidence of the virus that causes cold sores, even though most people who are infected with the virus have never developed signs and symptoms1.

A number of factors can trigger the development of a cold sore, including sunlight, sunburn, stress, fatigue, other infections, fever, menstruation and intestinal problems. While often difficult to single out, identifying a possible trigger may be useful in preventing recurring outbreaks 2.

Exposure to sunlight usually precedes the development of a cold sore by approximately 24-48 hours. Should a cold sore develop within a day or two of being in the sun, one can be fairly confident that sunlight is a “trigger” 2.

UVB radiation seems to reduce the effectiveness of the immune system. This means that for a person who suffers from cold sores, the body can no longer keep the virus at bay which can result in re-activation of the virus infection 3.

If sunlight seems to be a primary trigger for the development of cold sores, sunblock should be applied to the area where the cold sore tends to erupt 1.

Cold sores usually heal without leaving a scar 1. Once the blisters break, a crust forms over the resulting sore 1. While there is no cure for cold sores, some medications may relieve the pain, soften the crusts on the skin and resolve the cold sore faster 2,4.

An antiviral cream such as Acitop; the market leader in cold sores and fever blisters 5, prevents the virus from multiplying 6, helping to relieve the pain in as little as 2,9 days 7 and relieves a cold sore in 5 days7. It is suitable for children and adults and can be reapplied every four hours and should be started as early as possible

following onset of cold sore symptoms 6, 7*.

* Individual response may vary. If healing has not occurred, treatment can be continued for up to 10 days. For further information, speak to your healthcare professional

DISCLAIMER: This editorial has been commissioned and brought to you by iNova Pharmaceuticals. Content in this editorial is for general information only and is not intended to provide medical or other professional advice. For more information on your medical condition and treatment options, speak to your healthcare professional.



Scheduling status: S1 Proprietary Name (and dosage form): ACITOP cream. Pharmacological Classification: A 20.2.8. Antiviral agent. Composition: Each gram of cream contains 50 mg of Acyclovir. (5,0 % w/w Acyclovir). Preservative: Chlorocresol 0,12 % m/m. Reg. No. 32/20.2.8/0719. Marketed by: iNova Pharmaceuticals (Pty) Limited. Co. Reg. No. 1952/001640/07, 15E Riley Road, Bedfordview. Tel. No. 011 087 0000. For full prescribing information, refer to the package insert as approved by the SAHPRA (South African Health Products Regulatory Authority). Further information is available on request from iNova Pharmaceuticals. IN3029/18


  1. Mayo Clinic. Cold Sores. (2021) at
  2. University Health Science, University of Michigan. Cold and Canker Sores (2021) at
  3. World Health Organisation. Ultraviolet Radiation (UV) at
  4. Pringle, CR. Herpes Simplex Virus Infections. Merck Manual Consumer Version (2018) at
  5. IMS Data D6D Top Viral INF Products. November 2021
  6. Acitop approved package insert, June
  7. Spruance, S. L. et al. Acyclovir Cream for Treatment of Herpes Simplex Labialis: Results of Clinical Trials. Antimicrob. Agents Chemother. 46, 2238 -2243 (2002).