Cold sores are caused by the herpes simplex virus type 1 (HSV-1), a highly contagious pathogen resulting in small, fluid-filled blisters typically forming around the mouth and lips. While common and generally harmless in older children and adults, a baby can get a cold sore, and for an infant, this infection represents a serious medical emergency. A herpes infection in a newborn, known as Neonatal Herpes Simplex, is potentially life-threatening and requires immediate medical intervention. The infant’s underdeveloped defenses cannot contain the virus, allowing it to spread rapidly beyond the skin to vital organs and the nervous system.
Why Infants Are Highly Vulnerable
The danger of HSV-1 to a baby, particularly one under six weeks of age, stems from their immature immune system. Unlike older individuals, whose immune response localizes the virus, a newborn’s immune system lacks the ability to effectively wall off the virus, allowing it to travel through the bloodstream. This failure to contain the infection can lead to a systemic illness affecting multiple major organs, including the brain, lungs, and liver.
If the mother has pre-existing HSV antibodies, some passive immunity may be transferred through the placenta, offering temporary protection. Infants whose mothers acquire the infection late in pregnancy or who are exposed to the virus postnatally lack these protective antibodies, placing them at a much higher risk for the most severe forms of the disease.
How the Virus Spreads to Babies
The transmission of HSV-1 to an infant can occur in three main ways: during pregnancy, during delivery, or most commonly, after birth. Postnatal infection, which accounts for about 10% of neonatal cases, often happens through direct contact with a caregiver who has an active cold sore. The act of kissing an infant while having an active lesion is a well-documented cause of transmission.
The virus is also shed from the site of the lesion in the fluid of the blisters, and touching a sore and then touching the baby can spread the infection. A significant risk is asymptomatic viral shedding, where the virus is released from the skin or mucous membranes even when no visible cold sore or blister is present. A person can be contagious immediately before a blister appears or without ever developing a lesion. Strict hygiene measures are necessary for anyone with a history of cold sores, regardless of an active outbreak.
Recognizing Symptoms and Danger Signs
Identifying an HSV-1 infection in an infant can be challenging because initial symptoms are often vague and mimic other newborn illnesses. The infection may first appear as localized disease, presenting as small, fluid-filled blisters (vesicles) on the skin, eyes, or inside the mouth. These lesions may appear anywhere on the body, not just around the mouth, typically showing up within the first two weeks of life.
The most concerning development is the progression to systemic infection, known as Disseminated or Central Nervous System (CNS) disease. Signs of this widespread infection are often non-specific and include a general sepsis-like illness. Parents should watch for lethargy, poor appetite, and unusual irritability.
Other serious signs include a fever of 38°C (100.4°F) or higher, or conversely, a low body temperature, and breathing difficulties. If the infection has reached the brain, the baby may exhibit seizures or be unusually unresponsive. Any of these systemic signs in an infant under six weeks old, even without a blister, warrant an immediate trip to the emergency room.
Protecting Your Baby and Seeking Treatment
Preventing the spread of HSV-1 to an infant relies heavily on diligent hygiene and strict avoidance of direct contact when a lesion is present. Anyone with an active cold sore must avoid kissing the baby, and this restriction applies to the face, hands, and any other part of the infant’s body. Strict handwashing with soap and water is necessary before touching the baby, especially after touching one’s own mouth or an active lesion.
Caregivers who have a cold sore should consider wearing a surgical mask as an added precaution to minimize the risk of viral spread. If a herpes infection is suspected, medical treatment must be sought immediately, as delaying intervention significantly worsens the outcome. Treatment involves prompt hospitalization and the administration of high-dose intravenous antiviral medication, most commonly acyclovir.
The duration of intravenous treatment is determined by the extent of the infection: 14 days for localized skin, eye, or mouth disease, and 21 days for CNS or disseminated disease. Following initial hospital treatment, the infant often continues a six-month course of oral acyclovir to prevent recurrence and improve long-term neurological outcomes. This aggressive medical management is necessary because severe forms of Neonatal Herpes Simplex carry a risk of long-term disability or death, even with treatment.