Single Canker Sores/Cold Sores: these appear as a simple canker sore on the tongue, lip, or cheek inside the mouth. If on the outside of the mouth (such as a cold sore on the outer lip) you can try an OTC cold sore remedy (like Abreva). These are caused by herpes virus and are likely just a harmless mild flare up due to a past exposure. There is no known cure.
Multiple mouth sores and fever: this indicates more of an acute, painful, bothersome viral infection in the mouth that will cause your child to act fairly ill. The number one cause is Hand/Foot/Mouth virus, but it can also be cause by herpes virus. Here’s how to tell the difference:
Hand/Foot/Mouth Disease: this virus causes fever, canker sores that appear mostly in the back of the mouth, on the palate, and around the tonsils. There may be a few additional canker sores on the tongue and maybe inside the lips. There could also be crusty sores that appear on the face around the mouth. Blisters may also appear on the palms of the hands, soles of the feet, and in the diaper area. There will almost always be fever, which can last as long as a week. The sores may last 3 to 7 days. There is no medical treatment – eating cold/frozen food or drink and ibuprofen for pain and fever if needed can reduce the symptoms. It’s technically contagious for about 3 weeks through the saliva, although most schools allow a child to return a few days after the fever is gone and the sores are no longer painful (contagiousness is minimal by this point). There isn’t really a typical reason to be seen by a doctor to confirm this, since there’s no treatment. It’s usually obvious after a few days of symptoms once you see the sores in the mouth and the blisters show up on the hands or feet. These don’t always show up though, so it’s not always obvious.
Herpes Virus: this virus causes a distinctly different pattern of sores and can usually be distinguished from HFM disease based on this pattern. Herpes causes canker sores all over the front of the inside of the mouth and the gums. The gums will typically look swollen and red, and may even bleed. HFM disease, by contrast, almost never involves the gums and the sores are more in the back of the mouth. Herpes tends to cause worse pain and can last longer (7 to 10 days) and will often also have a fever. There is generally no medical treatment, but immunodeficient patients may be prescribed an anti-viral medication. It is contagious for as long as there are visible sores, excessive drooling, and swollen gums, and likely for several days more after these are all better. If an infant with herpes sucks on a finger or thumb, blisters may show up on that finger or thumb as well (in clusters of many sores – which look different that the more scattered HFM blisters on the palms). There typically isn’t a reason to be seen by a doctor for this, and second cases of this severe initial case as almost unheard of.
