Skin

Herpes Simplex (Cold Sores) in Babies

Content reviewed against published AAP, CDC, AAP, NIH guidelines

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Herpes simplex virus (HSV) causes painful blisters and sores on the skin and mucous membranes. HSV-1 typically causes oral herpes (cold sores) and is the more common type affecting children, while HSV-2 primarily causes genital herpes but can also infect newborns. In babies under 3 months old, herpes simplex is a medical emergency — neonatal herpes can cause devastating brain infection (encephalitis), organ failure, and death if not treated immediately with IV antivirals. In older babies and toddlers, HSV-1 typically presents as cold sores or gingivostomatitis (painful mouth sores) and is generally manageable.

Key takeaways

  • Herpes simplex virus (HSV) causes painful blisters and sores on the skin and mucous membranes.
  • Duration: Neonatal herpes requires 14-21 days of IV treatment followed by 6 months of oral suppressive therapy. Primary gingivostomatitis in older infants lasts 7-14 days, with the worst symptoms in the first 5-7 days. Individual cold sore recurrences last 7-10 days. HSV remains latent in nerve ganglia for life, with potential for periodic reactivation.
  • Go to ER if: Any baby under 3 months with a blister, vesicle, or fever — neonatal herpes must be ruled out immediately
  • No vaccine currently available

Symptoms

Painful, fluid-filled blisters or vesicles on or around the lips (cold sores)always
Painful mouth sores and swollen gums (gingivostomatitis in primary infection)common
Fever, especially during primary infectioncommon
Refusal to eat or drink due to mouth paincommon
Excessive droolingcommon
Irritability and fussinesscommon
Tingling or burning sensation before blisters appear (prodrome, in recurrences)sometimes
Swollen lymph nodes in the necksometimes
Herpetic whitlow — painful blisters on fingers from sucking (in babies who touch sores)rare

How It Presents by Age

0-3 months

MEDICAL EMERGENCY. Neonatal herpes can present in three patterns: (1) Skin, eye, and mouth disease (SEM) with vesicles on skin, eye redness, and mouth sores; (2) Central nervous system disease with seizures, lethargy, poor feeding, and irritability; (3) Disseminated disease with sepsis-like picture, liver failure, and multiorgan involvement. Fever may or may not be present. Skin vesicles may be absent in up to 40% of cases.

Risk level: VERY HIGH — neonatal herpes is life-threatening. Mortality is 30% for disseminated disease even with treatment. Untreated mortality exceeds 80%.

3-12 months

Primary HSV-1 infection most commonly presents as gingivostomatitis — widespread painful mouth ulcers, swollen gums that bleed easily, high fever, drooling, and refusal to eat or drink. Episodes are self-limiting but can lead to dehydration from poor oral intake. May also present as cold sores.

Risk level: Moderate — primary infection can be severe with dehydration risk. Very rarely progresses to encephalitis.

1-3 years

Gingivostomatitis is the most common presentation of primary HSV-1. Toddlers develop fever followed by painful oral ulcers, drooling, and irritability. Cold sores (herpes labialis) may occur as recurrences after the primary infection has resolved. Herpetic whitlow can develop from finger-sucking during active infection.

Risk level: Low to moderate

3-5 years

By this age, many children have been exposed to HSV-1. Primary infection may present as gingivostomatitis or as cold sores. Recurrent cold sores are triggered by illness, sun exposure, or stress. Children with eczema are at risk for eczema herpeticum — widespread herpes on eczematous skin.

Risk level: Low for typical cold sores. Moderate if child has eczema (risk of eczema herpeticum).

Treatment

IV acyclovir (neonatal herpes)

Neonatal herpes is treated with high-dose IV acyclovir (60 mg/kg/day) for 14-21 days depending on the extent of disease. This is a medical emergency requiring immediate hospitalization. Suppressive oral acyclovir follows for 6 months to reduce recurrence and improve neurodevelopmental outcomes.

Oral acyclovir/valacyclovir (gingivostomatitis)

Oral acyclovir started within 72 hours of symptom onset can reduce the duration and severity of primary gingivostomatitis. Dosing is typically 15 mg/kg 5 times daily for 7 days.

Pain management

Acetaminophen or ibuprofen (6 months and older) for pain and fever. A mixture of liquid antacid and diphenhydramine (magic mouthwash) may be swabbed on mouth sores for topical relief. Cold foods and popsicles can soothe mouth pain.

Hydration support

Dehydration is the most common complication of gingivostomatitis. Offer cool fluids frequently. Avoid acidic or salty foods. If the child cannot maintain hydration orally, IV fluids may be needed.

Topical antivirals for cold sores

Topical acyclovir or penciclovir cream applied at the first sign of tingling may shorten recurrent cold sore duration by 1-2 days. Less effective than oral antivirals.

Home Care

  • Offer cool fluids, popsicles, and smoothies to maintain hydration during mouth sores
  • Avoid acidic (citrus, tomatoes), salty, or spicy foods that irritate mouth sores
  • Apply petroleum jelly or lip balm to cold sores to prevent cracking and ease discomfort
  • Use acetaminophen or ibuprofen as directed for pain relief
  • Offer soft, cool foods such as yogurt, applesauce, or mashed banana
  • Apply a cool, damp washcloth to cold sores for comfort

When to Worry

Go to the ER if:

  • Any baby under 3 months with a blister, vesicle, or fever — neonatal herpes must be ruled out immediately
  • Seizures in a child with suspected herpes infection
  • Extreme lethargy, poor feeding, or inconsolability in a young infant
  • Signs of severe dehydration — sunken fontanelle, no wet diapers for 6+ hours, no tears
  • Vesicles spreading to the eye with redness, swelling, or discharge (herpes keratitis)
  • Rapidly spreading vesicles on a child with eczema (eczema herpeticum)
  • Newborn with sepsis-like picture — mottled skin, rapid breathing, temperature instability

Call your doctor if:

  • Suspected first episode of cold sores or mouth sores in a child under 12 months
  • Mouth sores making it difficult for the child to drink
  • Fever lasting more than 3 days with mouth sores
  • Cold sores near the eye or on the eyelid
  • Frequent recurrences of cold sores (more than 6 per year)
  • Child with eczema develops new vesicles or worsening of eczema patches
  • Signs of dehydration — decreased urination, dry mouth, no tears when crying

Keep an eye on:

  • Any vesicle, blister, or sore on a baby under 3 months old — treat as an emergency
  • Child with mouth sores is refusing all fluids for more than 8 hours
  • Decreased wet diapers (fewer than 3 in 24 hours) indicating dehydration
  • High fever lasting more than 5 days
  • Vesicles spreading to the eye area
  • Child with eczema develops rapidly spreading vesicles on eczematous skin (possible eczema herpeticum)
  • Seizures, extreme lethargy, or unusual sleepiness

Prevention

  • NEVER kiss a baby on or near the mouth, hands, or face if you have an active cold sore
  • Wash hands thoroughly before handling a newborn
  • Do not allow anyone with an active cold sore to hold or kiss a baby under 3 months
  • Inform your obstetrician if you or your partner have a history of genital herpes, as cesarean delivery may be indicated for active lesions at the time of birth
  • Avoid sharing utensils, cups, lip balm, or towels with someone who has cold sores
  • Teach older children not to touch their cold sores and to wash hands frequently
  • Apply sunscreen or lip balm with SPF to reduce sun-triggered recurrences in older children

Contagion & Incubation

Incubation

Neonatal herpes: typically 2 days to 2 weeks after birth (can present up to 6 weeks). Primary oral herpes (gingivostomatitis) in older infants: 2-12 days after exposure. Recurrent cold sores appear 1-3 days after trigger exposure.

Contagious for

Most contagious when active sores are present and weeping. However, HSV can be shed asymptomatically, meaning transmission can occur even without visible sores. Contagious from the tingling/prodromal phase through complete crusting and healing of blisters.

Duration

Neonatal herpes requires 14-21 days of IV treatment followed by 6 months of oral suppressive therapy. Primary gingivostomatitis in older infants lasts 7-14 days, with the worst symptoms in the first 5-7 days. Individual cold sore recurrences last 7-10 days. HSV remains latent in nerve ganglia for life, with potential for periodic reactivation.

Frequently asked questions

How long does herpes simplex (cold sores) last?
Neonatal herpes requires 14-21 days of IV treatment followed by 6 months of oral suppressive therapy. Primary gingivostomatitis in older infants lasts 7-14 days, with the worst symptoms in the first 5-7 days. Individual cold sore recurrences last 7-10 days. HSV remains latent in nerve ganglia for life, with potential for periodic reactivation.
How does herpes simplex virus (hsv) spread?
HSV spreads through direct contact with an active sore, saliva, or skin that is shedding the virus (asymptomatic shedding). Newborns most commonly acquire HSV during passage through an infected birth canal, but can also be infected after birth through kissing, skin contact with active cold sores, or contact with contaminated hands. Adults and children with cold sores can transmit the virus to babies through seemingly innocent contact such as kissing.
When should I take my baby to the ER?
Any baby under 3 months with a blister, vesicle, or fever — neonatal herpes must be ruled out immediately. Seizures in a child with suspected herpes infection. Extreme lethargy, poor feeding, or inconsolability in a young infant. Signs of severe dehydration — sunken fontanelle, no wet diapers for 6+ hours, no tears. Vesicles spreading to the eye with redness, swelling, or discharge (herpes keratitis). Rapidly spreading vesicles on a child with eczema (eczema herpeticum). Newborn with sepsis-like picture — mottled skin, rapid breathing, temperature instability
Can herpes simplex virus (hsv) be prevented?
NEVER kiss a baby on or near the mouth, hands, or face if you have an active cold sore. Wash hands thoroughly before handling a newborn. Do not allow anyone with an active cold sore to hold or kiss a baby under 3 months. Inform your obstetrician if you or your partner have a history of genital herpes, as cesarean delivery may be indicated for active lesions at the time of birth. Avoid sharing utensils, cups, lip balm, or towels with someone who has cold sores. Teach older children not to touch their cold sores and to wash hands frequently. Apply sunscreen or lip balm with SPF to reduce sun-triggered recurrences in older children
When can my child return to daycare?
Children with cold sores do not need to be excluded from school or daycare. They should avoid kissing other children, sharing utensils or cups, and should wash hands frequently. Children with gingivostomatitis can return once fever has resolved and they are able to eat and drink comfortably, though the virus may still be shed in saliva.

Sources

AAPCDCAAPNIH

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources

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Bottom line

Herpes Simplex (Cold Sores) is a viral illness that typically resolves on its own. Seek emergency care if any baby under 3 months with a blister, vesicle, or fever — neonatal herpes must be ruled out immediately.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.