Sunlight & Cold Sores

Cold sores are caused by the herpes simplex 1 virus, which people usually catch in childhood or early adulthood, says the American Dental Association. The first outbreak may cause fever and mouth ulcers and some people go on to develop cold sores in later life. A number of different health and environmental conditions can cause cold sores to recur; one of them is overexposure to sunlight.

About Cold Sores

After the first outbreak, cold sores most often appear as small, painful, fluid-filled blisters on the lips, but you can also get them on your nostrils, says the American Dental Association. The blisters usually dry out to form a yellow crust which heals within two weeks. However, they can keep coming back and most sufferers have on average two outbreaks a year.

Catching the Cold Sore Virus

You catch the herpes simplex 1 by coming into contact with the body fluids, such as saliva, of someone who already has the virus, says the Encyclopedia of Children’s Health. Cold sores are extremely contagious and the blisters don’t have to be present for someone with the virus to pass on the infection. In fact, says Colgate World of Care, most children catch the virus and, while it remains in the system for life, only about a quarter of carriers go on to have outbreaks as adults.

Sunlight As a Cold Sore Trigger

According to the Encyclopedia of Children’s Health, the virus remains dormant in the nerve cells of your face where the immune system can’t find and fight it. And, while the University of Maryland Medical Center says it is not completely known what causes cold sores to recur, they usually reappear when you are ill and your immune system is run down. The obvious triggers are a cold, injury, or stress, but medical professionals also believe that ultraviolet (UV) radiation—that is, exposure to the sun—can cause cold sores to flare up.

About Ultraviolet Radiation

UV radiation is one of the ingredients of sunlight and its strength is determined by a number of factors, including cloud cover, how close you are to the equator and elevation—UV rays are more potent the higher up you go, says the World Health Organization. In small doses, UV radiation is good for you because it helps your body produce vitamin D, but it’s no secret that too much can cause sunburn and lead to premature aging and skin cancers. What is less known, says the World Health Organization, is that overexposure to UV radiation can impair your immune system and slow down its infection-fighting responses, which is why too much sun can trigger a cold sore.


Because cold sores usually recur when your body is rundown, taking care of yourself is the best way to fend off infection. If your outbreaks tend to follow a day in the sun, Colgate World of Care says there is evidence that applying sunscreen to your lips may prevent cold sores from appearing, and avoid sitting in the sun to the point of getting burnt. To stay at your infection-fighting best, also try to eat healthily and get a decent night’s sleep. If you do get a cold sore, the American Dental Association says over-the-counter topical anesthetics can provide some relief from the painful blisters.