Herpetic Gingivostomatitis (Mouth Sores) in Babies
The short answer
Herpetic gingivostomatitis is a common first-time infection with the herpes simplex virus (HSV-1) that causes painful sores on the gums, tongue, lips, and inside the cheeks. It is most common in children between 6 months and 5 years. While the sores look alarming and can make eating very painful for several days, the infection resolves on its own within 7-14 days. The main concern is keeping your child hydrated while their mouth is sore.
By Age
What to expect by age
HSV infection in babies under 6 months is uncommon but can be more serious due to their immature immune system. Neonatal herpes (contracted during birth) is a separate, more urgent condition. If a very young baby develops mouth sores with fever, seek medical evaluation promptly. Avoid kissing a baby if you have an active cold sore.
This is a common age for a first HSV-1 infection, often acquired from a family member's cold sore through kisses or shared utensils. The infection starts with a fever of 102-104F (39-40C), followed by painful sores appearing on the gums, tongue, and inner cheeks. Gums may become very red, swollen, and bleed easily. Your baby will likely drool heavily and refuse to eat. Cool liquids, cold foods, and pain medication can help.
Toddlers with gingivostomatitis may have 10-20 painful ulcers in the mouth at once. They will often refuse all food and most drinks. Popsicles, cold milk, yogurt, and smoothies are often better tolerated than warm foods. The worst pain is typically days 2-5, with gradual improvement after that. After this primary infection, the virus stays dormant and may occasionally cause cold sores later in life.
What Should You Do?
When to take action
- Multiple small, shallow ulcers on the gums, tongue, and inner cheeks during the first HSV-1 infection
- High fever (102-104F / 39-40C) for 3-5 days at the start of the illness
- Heavy drooling and refusal to eat due to mouth pain
- Swollen, red gums that may bleed when touched
- Sores that take 7-14 days to fully heal
- Your child is drinking very little and you are concerned about dehydration
- Fever persists beyond 5-7 days
- Mouth sores have not started to heal after 10 days
- Your child has recurrent episodes of mouth sores
- Your child shows signs of dehydration: no wet diapers for 6+ hours, no tears, sunken fontanelle, or dry mouth
- A baby under 3 months develops any mouth sores or blisters with fever
- Your child has sores near or in the eyes, which can cause serious eye infection
- Your child has a weakened immune system and develops mouth sores
- Your child becomes very lethargic, difficult to wake, or has a stiff neck
Sources
Related Resources
Related Medical Concerns
Baby Oral Thrush (Mouth Yeast Infection)
Oral thrush is a common yeast infection (Candida) that causes creamy white patches on the tongue, gums, and inner cheeks. Unlike milk residue, thrush patches do not easily wipe away. It is very common in babies under 6 months, is usually mild, and is easily treated with a prescribed antifungal medication.
Hand, Foot, and Mouth Disease in Babies
Hand, foot, and mouth disease (HFMD) is a very common viral illness in babies and toddlers, especially during summer and fall. It causes small blisters or sores in the mouth and a spotted rash on the hands and feet. While it can make your child uncomfortable for a few days, it is not dangerous and resolves on its own within 7-10 days.
Baby White Tongue - Milk Residue or Thrush?
A white tongue in babies is extremely common and is usually just milk residue from breastfeeding or formula feeding. Milk residue coats the tongue lightly and can be wiped away with a damp cloth. Thrush (oral candidiasis) is a yeast infection that creates white patches that look like cottage cheese and do NOT wipe away easily - if you try, the tissue underneath may appear raw or bleed. Thrush can also appear on the cheeks, gums, and roof of the mouth.
Is My Baby Dehydrated?
Dehydration in babies happens when they lose more fluids than they take in, usually from vomiting, diarrhea, fever, or inadequate feeding. Key signs include fewer than six wet diapers in 24 hours, no tears when crying, a dry mouth, sunken fontanelle (soft spot), and unusual drowsiness. Mild dehydration can often be managed at home with extra fluids, but moderate to severe dehydration requires prompt medical attention.
My Baby's Head Shape Looks Abnormal
Many babies develop temporary head shape irregularities that are completely normal. A cone-shaped head from vaginal delivery reshapes within days. Mild positional flattening (plagiocephaly) from sleeping on the back is very common and usually improves with repositioning and tummy time. However, head shape changes involving ridges, a persistently bulging fontanelle, or rapid head growth changes should be evaluated to rule out craniosynostosis.
I'm Worried About Lazy Eye (Amblyopia)
Amblyopia (lazy eye) is the most common cause of vision loss in children, affecting about 2-3% of kids. It occurs when one eye develops weaker vision because the brain favors the other eye. The tricky part is that amblyopia often has no obvious outward signs - the eye usually looks normal. Early detection through routine vision screening is critical because treatment is most effective in the first few years of life.