Many parents are alarmed the first time they see a cluster of cold sores around their child's mouth, particularly if it is accompanied by the dramatic mouth ulceration that can occur with primary herpes simplex infection. The illness looks frightening. In most healthy children beyond early infancy, it resolves without treatment, though it can take a week or two.
The important exceptions are newborns, in whom herpes simplex can be a life-threatening infection, and immunocompromised children, who need prompt antiviral treatment. Knowing which situation you are in changes the response considerably.
Healthbooq (healthbooq.com) covers common childhood illnesses and infections through the early years.
What Cold Sores Are
Herpes simplex virus type 1 (HSV-1) causes cold sores. It is one of the most prevalent human viruses globally, infecting around two-thirds of adults under 50 worldwide according to WHO data. Infection is lifelong: the virus establishes latency in nerve cells and cannot be eliminated from the body, but most people have long periods without any symptoms at all.
The virus spreads through direct contact with infected saliva or skin lesions. Children typically acquire it from kisses from a parent or relative who carries the virus, often without knowing they are infectious at the time. This is uncomfortable to learn when it has just made a toddler miserable, but it is a reflection of how common the virus is rather than any particular carelessness.
Primary Infection
The first time HSV-1 infects a child who has no prior immunity, the response can be considerably more pronounced than a typical cold sore outbreak. Primary herpetic gingivostomatitis is the clinical term for this. It involves painful ulcers on the gums, tongue, inner cheeks, and lips, fever, irritability, swollen lymph nodes in the neck, and often refusal to eat or drink due to pain.
This can look alarming. The mouth ulcers bleed easily and the child may drool extensively. It typically lasts seven to ten days and resolves without specific antiviral treatment in healthy children with intact immune systems.
The main concern during primary infection is dehydration. A child who is refusing all food and drink due to mouth pain needs encouragement to take fluids. Ice lollies, ice chips, cold drinks, and soft foods at cool temperatures all help. Paracetamol or ibuprofen for pain and fever, given regularly at appropriate doses, makes a real difference to the child's comfort and willingness to drink.
If a child cannot maintain adequate fluid intake, becomes very unwell, or shows signs of dehydration (very dry mouth, sunken eyes, not passing urine), see a GP or seek assessment at an urgent care centre.
Oral aciclovir, prescribed by a GP, can reduce the duration of primary infection if started within 72 hours of onset. For a very unwell child, it is worth asking about this.
Subsequent Outbreaks
After the primary infection, most people have occasional recurrences. These are typically much milder: a tingling or burning sensation followed by a blister or cluster of blisters on or near the lip, which crusts over and heals within a week or so. They are triggered by fever, illness, UV exposure, fatigue, and stress.
Over-the-counter aciclovir cream (Zovirax and other brands) applied at the earliest sign of a tingling can reduce outbreak duration. Once the blister has formed it is less useful but still worth applying. It cannot eliminate the virus.
Cold sores are contagious from the moment the tingling starts until the crust has fully healed. During this time, kissing and sharing utensils or cups should be avoided. Children with active cold sores should be kept away from newborns and from anyone who is immunocompromised.
Cold Sores in Newborns: A Different Situation
Neonatal herpes is rare but serious. Newborns have immature immune systems and cannot contain the virus effectively. Infection can spread to the brain, eyes, and internal organs.
A newborn with any blisters on the skin, particularly if accompanied by fever, lethargy, poor feeding, or irritability, needs urgent medical assessment. If a newborn has been exposed to an active cold sore, tell the midwife or neonatal team immediately.
The risk is higher if the mother has a primary genital HSV infection near delivery, but can occur with contact from anyone carrying the virus. Most cases of neonatal herpes occur when the mother has no known HSV history. Do not kiss a newborn if you have an active cold sore. Anyone visiting a newborn with an active cold sore should avoid any mouth contact with the baby.
When to See a GP
For healthy children beyond the newborn period, see a GP if the child is significantly dehydrated, if the illness is not resolving after 10 to 14 days, if the eye is affected (a red painful eye with a cold sore nearby needs urgent assessment as HSV keratitis can affect vision), or if the child is immunocompromised for any reason.
Key Takeaways
Cold sores are caused by herpes simplex virus type 1 (HSV-1), which infects the majority of adults worldwide, usually acquired in childhood. The primary infection is often a more severe illness than subsequent outbreaks, sometimes causing significant mouth ulceration (gingivostomatitis) with fever and difficulty eating. Subsequent outbreaks are generally milder and represent reactivation of virus that remains latent in nerve tissue. Cold sores in newborns are a medical emergency. In immunocompetent children beyond the newborn period, cold sores are uncomfortable but rarely dangerous; aciclovir cream can reduce duration if applied early in an outbreak.
