What does this mean?
The lining inside the mouth is not as tough against infection as skin is. Small fluid-filled blisters form first; they burst within a short time and leave behind shallow sores with red edges that hurt a great deal when touched. A fever, by contrast, is the whole body responding rather than one small area. When widespread sores and a fever appear together, what is going on is not confined to the spot where a tooth is coming through.
What tells them apart is where the sores are and when the fever started. With teething, the gum swells and becomes tender only at the point where the tooth is due; dribbling increases, your child bites on everything, and the temperature usually stays mild. If instead the whole gum margin is swollen and bright red, if the sores have spread to the tongue, the inside of the cheeks and the inner surface of the lip, and if there is a noticeable smell in the mouth and a fever that began before the sores, teething does not explain the picture.
The sores themselves are not all alike. In an older child, one or two round sores on the tongue or inside the lip with no fever point more towards recurrent mouth ulcers. In a young child, a widespread picture appearing for the first time, coming with a fever and involving the gums as well, most often comes down to a first encounter with a virus. If there is also a rash on the hands, feet and buttocks, that is a separate picture and a paediatrician should see your child. Whatever it turns out to be called, what matters in the first few days is how much fluid your child can take.
Widespread mouth sores together with a fever can have several different causes; the headings below are the ones a clinician thinks of first, and this list does not stand in for a diagnosis.
Likely causes
What helps at home?
- Put fluids first. Cold water, milk, yoghurt drinks, yoghurt and ice cream take the edge off the pain; offer them in small amounts and often. If drinking from a cup stings, a straw may help.
- Take sour, salty, spicy and hot food off the menu for a few days. Orange juice, tomatoes, crisps and hot soup noticeably increase the pain when they touch the sores.
- Do not put lemon, salt, bicarbonate of soda, cologne or a crushed painkiller on the sores, and do not use numbing gels without asking a clinician first. Rather than stopping brushing altogether, carry on with a soft brush, keeping away from the sores.
- Keep cups, towels, dummies and bottles separate, and wash hands often. Your child should not rub their eyes after touching the sores. While the fever lasts and new sores are still appearing, keep your child at home rather than sending them to nursery.
- Your child has drunk nothing for hours; is passing less urine, a baby's nappy has stayed dry for half a day, or there are no tears when crying
- Your child stays drowsy even after the fever has been brought down, is becoming harder to wake, or the fever lasts longer than three days
- Your child cannot open their mouth or swallow, saliva is running out uncontrollably, the voice has changed, or breathing has become difficult
- There is swelling on the face, under the jaw or in the neck, or your child struggles to move their neck
- Redness, watering and discomfort in bright light have started in the eye, or a baby with a fever is under three months old
Frequently asked questions
- Could it just be teething?
- Teething causes swelling at a single point on the gum, more dribbling and restlessness, and the temperature usually stays mild. If there are sores in several places in the mouth at once and the fever has climbed noticeably, teething does not explain the picture. Putting a fever down to teething and waiting is one of the common reasons children end up short of fluids.
- Can it pass to a sibling or to us?
- The versions of this caused by a virus can spread through saliva, so it makes sense to keep cups, towels, dummies and bottles separate and to wash hands often. In a young child meeting the virus for the first time the picture is noisier; in older people who have met it before it most often shows up as a cold sore at the edge of the lip. Ordinary mouth ulcers, on the other hand, are not contagious.
- Should we see a paediatrician or a dentist?
- When a fever and widespread sores come together, a paediatrician should see your child first; fluid intake and the fever are assessed there. A dentist looks at where the sores are and how they appear, and checks whether a broken tooth, a wire or irritation from a newly erupted tooth is part of the story. If a single sore is left once the fever has passed and it has not healed within two weeks, that sore needs to be assessed separately.
This content is for general information and does not replace an in-person examination. Symptoms overlap between conditions, and a diagnosis can only be made clinically.