Cold Sores (Herpes Simplex) on Baby
Medically reviewed by Dr. Sarah Chen, MD, FAAP · Board-Certified Pediatrician
Content reviewed against published AAP, CDC, NIH guidelines
Last reviewed:
Baby skin is sensitive and changes frequently. If you are noticing cold sores (herpes simplex) on baby, here is what you need to know.
The short answer
Cold sores are caused by herpes simplex virus (HSV) and can be very dangerous for newborns under 3 months old. In older babies and toddlers, a first cold sore infection may cause painful mouth sores and fever but is usually manageable. Never kiss a baby when you have an active cold sore, and seek immediate medical attention if a newborn is exposed.
Key takeaways
- Cold sores are caused by herpes simplex virus (HSV) and can be very dangerous for newborns under 3 months old. In older babies and toddlers, a first cold sore infection may cause painful mouth sores and fever but is usually manageable. Never kiss a baby when you have an active cold sore, and seek immediate medical attention if a newborn is exposed.
- Usually normal when: A recurrent cold sore on the lip of a toddler that is small, healing on its own, and not near the eyes
- Call your doctor if: Any blisters, fever, or illness in a baby under 6 weeks who may have been exposed to HSV requires emergency evaluation
- Varies by age — see the age-by-age breakdown below
“Eczema is very common in babies and children. About 1 in 10 children will develop eczema, typically starting in the first few months of life.”
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What Parents Should Know
According to AAP, CDC, NIH guidelines, cold sores are caused by herpes simplex virus (HSV) and can be very dangerous for newborns under 3 months old. In older babies and toddlers, a first cold sore infection may cause painful mouth sores and fever but is usually manageable. Never kiss a baby when you have an active cold sore, and seek immediate medical attention if a newborn is exposed. At 0-3 months, herpes simplex virus is extremely dangerous in newborns because their immune systems cannot fight it effectively. Neonatal herpes can cause serious brain, organ, and skin damage. If a newborn develops blisters, fever, poor feeding, or lethargy, especially if exposed to someone with a cold sore, seek emergency medical care immediately. It is generally considered normal when a recurrent cold sore on the lip of a toddler that is small, healing on its own, and not near the eyes. However, you should contact your pediatrician promptly if any blisters, fever, or illness in a baby under 6 weeks who may have been exposed to HSV requires emergency evaluation.
Normal vs. Concerning
By Age
What to expect by age
0-3 months
Herpes simplex virus is extremely dangerous in newborns because their immune systems cannot fight it effectively. Neonatal herpes can cause serious brain, organ, and skin damage. If a newborn develops blisters, fever, poor feeding, or lethargy, especially if exposed to someone with a cold sore, seek emergency medical care immediately.
3-6 months
While still a concern, herpes simplex in babies beyond the neonatal period is typically less severe. A primary HSV infection may cause gingivostomatitis with painful sores inside the mouth, fever, drooling, and refusal to eat. Pain management and hydration are key. Contact your pediatrician if you suspect HSV infection.
6-12 months
As babies explore and are kissed by more family members, exposure risk increases. Primary herpes gingivostomatitis can cause significant discomfort for 7 to 10 days. Offer cold fluids and soft foods, and use pain medication as recommended by your pediatrician. The virus then goes dormant and cold sores may recur periodically.
12-24 months
Toddlers may have their first HSV exposure at daycare from shared toys and cups. Recurrent cold sores are milder than the first outbreak and usually appear on the lips. Keep cold sore areas clean and avoid touching other parts of the body, especially the eyes. Cold sores near the eye need urgent medical evaluation.
What to Tell Your Pediatrician
- Describe when you first noticed cold sores (herpes simplex) on baby and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if a first-time outbreak of mouth sores with fever and difficulty eating.
- Mention if your baby was exposed to someone with an active cold sore.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
What Should You Do?
When to take action
- A recurrent cold sore on the lip of a toddler that is small, healing on its own, and not near the eyes
- A first-time outbreak of mouth sores with fever and difficulty eating
- Your baby was exposed to someone with an active cold sore
- Recurrent cold sores that are frequent or spreading
- Any blisters, fever, or illness in a baby under 6 weeks who may have been exposed to HSV requires emergency evaluation
- Cold sores near the eye, which can cause a serious eye infection
- Widespread blisters over eczema patches, suggesting eczema herpeticum
- A baby with cold sores who becomes lethargic, has a high fever, or stops feeding
What You Can Do at Home
- Keep track of when you notice cold sores (herpes simplex) on baby — noting the time of day, duration, and any triggers can help your pediatrician.
- Remember that a recurrent cold sore on the lip of a toddler that is small, healing on its own, and not near the eyes — this is generally within the range of normal.
- At 0-3 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
- Use fragrance-free, hypoallergenic products on your baby's skin. Avoid over-bathing — 2-3 baths per week is usually sufficient.
- While monitoring at home, seek immediate care if any blisters, fever, or illness in a baby under 6 weeks who may have been exposed to HSV requires emergency evaluation.
Related Conditions
Baby Blistering Rash (Fluid-Filled Blisters)
Fluid-filled blisters on a baby's skin can be caused by many things, including hand-foot-and-mouth disease, friction burns, insect bites, impetigo, chickenpox, or herpes simplex. While many causes are mild, blistering rashes in young babies or those accompanied by fever should be evaluated by a doctor to determine the cause and best treatment.
Signs of Infected Eczema in Baby
Eczema skin is more vulnerable to infection because the skin barrier is compromised. Signs of infected eczema include yellow or honey-colored crusting, oozing pus, increased redness and warmth, worsening pain, and fever. Infected eczema needs treatment with antibiotics and should be evaluated by your pediatrician promptly.
Related Resources
Baby Skin Conditions Guide
Visual guide to common baby skin conditions, rashes, and when to see a doctor.
Month-by-Month Development
Detailed monthly development guides from birth through 24 months.
When to Call the Doctor
General guide on when to call the pediatrician, visit urgent care, or go to the ER.
Frequently asked questions
Is cold sores (herpes simplex) on baby normal?
When should I call the doctor about cold sores (herpes simplex) on baby?
When is cold sores (herpes simplex) on baby normal?
What causes cold sores (herpes simplex) on baby?
What should I mention to my pediatrician about cold sores (herpes simplex) on baby?
Is cold sores (herpes simplex) on baby normal at 0-3 months?
Is cold sores (herpes simplex) on baby normal at 3-6 months?
Should I go to the ER for cold sores (herpes simplex) on baby?
Does cold sores (herpes simplex) on baby go away on its own?
References
Doctor Visit Checklist
Bring this checklist to your next pediatrician visit to discuss Cold Sores (Herpes Simplex) on Baby.
Things to mention
- Describe when you first noticed cold sores (herpes simplex) on baby and how it has changed over time.
- Note your baby's current age and which age-specific patterns you are seeing.
- Mention if a first-time outbreak of mouth sores with fever and difficulty eating.
- Mention if your baby was exposed to someone with an active cold sore.
- Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
- Bring a list of any questions or observations you want to discuss at the appointment.
Observations to share
- A first-time outbreak of mouth sores with fever and difficulty eating
- Your baby was exposed to someone with an active cold sore
- Recurrent cold sores that are frequent or spreading
Urgent signs to report immediately
- Any blisters, fever, or illness in a baby under 6 weeks who may have been exposed to HSV requires emergency evaluation
- Cold sores near the eye, which can cause a serious eye infection
- Widespread blisters over eczema patches, suggesting eczema herpeticum
My notes
From ismybabyalright.com — free, evidence-based baby health guides
All content follows our editorial policy and is reviewed against published clinical guidelines.
2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members
Related Resources
Bottom line
Most cases of cold sores (herpes simplex) on baby are normal. Talk to your pediatrician if any blisters, fever, or illness in a baby under 6 weeks who may have been exposed to hsv requires emergency evaluation.
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.
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Related Skin Concerns
Baby Blistering Rash (Fluid-Filled Blisters)
Fluid-filled blisters on a baby's skin can be caused by many things, including hand-foot-and-mouth disease, friction burns, insect bites, impetigo, chickenpox, or herpes simplex. While many causes are mild, blistering rashes in young babies or those accompanied by fever should be evaluated by a doctor to determine the cause and best treatment.
Signs of Infected Eczema in Baby
Eczema skin is more vulnerable to infection because the skin barrier is compromised. Signs of infected eczema include yellow or honey-colored crusting, oozing pus, increased redness and warmth, worsening pain, and fever. Infected eczema needs treatment with antibiotics and should be evaluated by your pediatrician promptly.
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