Ask the Doctor: ‘I’ve broken out in very painful cold sores. Is this a symptom of long Covid?’

“I’ve had Covid more than one time and still feel the effects of it months later, but after the most recent time, I started developing severe cold sores around my mouth. It started off as just general dryness and peeling, but then my lips began swelling and the itchiness set in. I’ve never suffered from cold sores before and haven’t changed anything in my routine that would explain how I got them. Is this a symptom of long Covid?”

Answer from Professor Seamus Linnane, deputy medical director of the Beacon Hospital and consultant in respiratory & general internal medicine.

So many people have had Covid-19 at this stage that it is becoming increasingly difficult to separate long Covid symptoms from other illnesses. We have repeatedly seen patients attending our service with new symptoms after a Covid infection that turn out to be a separate disease altogether. The WHO recognises this problem and defines long Covid as symptoms that cannot be explained by another diagnosis. A second challenge for patients and doctors alike is the huge number of symptoms that long Covid causes. Based on my experience with patients, we have counted over 50 different symptoms. 

In your case, the symptoms seemed to lead on directly from your Covid infection and that’s certainly a feature we look for. You mention dryness, itching and peeling of the lips. Herpes Simplex Virus which is responsible for cold sores can cause this. Usually, however, there is an associated blistering rash that is often concentrated on the mouth. The rash is often painful and can spread to other parts of the mouth and face. The infection can also be transmitted to the genital area. It’s not clear whether you have the typical rash and a check by your GP should quickly confirm whether this is a recurrent Herpes infection. 

A large proportion of adults have had a Herpes infection at some point. Once the rash settles, the infection lays dormant and can return later when the body is under physical stress such as after a Covid-19 infection. Therefore, it is entirely possible that recurrent cold sores are a feature of long Covid in your case. It would be unusual for it to be the only symptom, however. Most patients with long Covid have more than one symptom such as fatigue, breathlessness and brain fog to mention some of the common ones. I would expect you to have some of these or other symptoms at the same time to blame your recurrent cold sores on long Covid. It is worth considering if there is something else putting your system under stress and allowing the cold sores to repeatedly flare-up. 

Finally, if you are not suffering frequent Herpes infections, the symptoms you describe could also be due to other conditions such as allergy or vitamin deficiency and blood tests may be needed to identify these.

In summary, yes cold sores can flare up after a Covid-19 infection. Usually, they go away as you get over the infection. Persistent recurrent cold sores are not a usual presentation of long Covid in the absence of other symptoms. It is advisable that you book a check-up with your GP to confirm that these symptoms are indeed cold sores and there is no other reason for them to be troubling you so much recently.