Medical Q&As

Cold sores - triggered by sunlight?

Every time I go on a sun holiday I get really bad cold sores. I have gone to the doctor about this and was prescribed Zovirax tablets and various creams. I was wondering if there was any way to prevent this. I have used sunblock on my lips but this doesn’t seem to prevent it happening.

Many people get cold sores after exposure to strong sunlight. It is thought that UV radiation can affect the immune system and that in the case of cold sores the immune system is no longer able to keep the Herpes Simplex virus under control, which results in a reactivation of the cold sore eruption. It is important to realise that the various tablets and creams you have tried in the past do not eliminate the virus from the body but simply cure the acute eruption. You are on the right track in using a sunblock on your lips and skin because experience shows that this does make a difference for many sufferers of cold sores. It is generally recommended that you use a sunblock of factor 25 or higher in order to prevent the eruption. Perhaps the sunblock you used in the past might not have had a sufficiently high protection factor. Also, the antiviral treatments for cold sores need to be applied before the lesions erupt on the lips or skin. You should bring one of those creams with you on holidays and apply it at the earliest opportunity when you feel the skin tingling rather than waiting for the blisters to develop.