What Do Neonatal HSV Blisters Look Like? Warning Signs

Neonatal herpes simplex virus (HSV) skin lesions classically appear as small, grouped, fluid-filled blisters (called vesicles) that sit on a reddened area of inflamed skin ^[1][2]. However, these blisters can change shape over time, and some infants are born with atypical rashes like open sores or crusted patches ^[3].

Importantly, you cannot diagnose HSV just by looking at a rash. Many harmless newborn rashes, as well as bacterial infections, can look identical to HSV. Because neonatal HSV can be serious, any newborn with a new blister, pustule, or unexplained open sore needs immediate, same-day medical evaluation ^[4]. Do not pop the blisters, do not apply home creams, and do not wait to see if the rash spreads or if the baby becomes ill. Always wash your hands before and after touching the baby.

The Classic Appearance

When a newborn develops visible skin signs of HSV, the rash typically has the following characteristics:

• Grouped Blisters (Vesicles): The lesions often start as small bumps filled with clear or cloudy fluid ^[1]. They usually appear in clusters rather than being spread evenly across the body ^[2].
• Reddened Base: The blisters frequently sit on top of an area of red, inflamed skin ^[1].

How the Rash Changes

HSV blisters on a newborn’s skin do not stay the same; they evolve over time. Depending on when you notice them, they might look like:

• Pustules: The fluid inside the blister may turn cloudy or pus-like ^[1][5].
• Punched-Out Erosions: The blisters can pop, leaving behind shallow, circular open sores ^[5][1].
• Crusts and Scabs: As the open sores heal, they can form crusted patches or plaques ^[3][6].

Congenital vs. Perinatal Infection

Most neonatal HSV is acquired during delivery (perinatal infection) and symptoms typically appear a few days to a few weeks after birth.

In rare cases, the infection occurs in the womb (congenital HSV). These babies are often born with atypical skin findings instead of classic blisters. They may have open sores, deep ulcers, thin sunken scars (atrophic patches), or changes in skin color present at birth ^[6][3]. In these congenital cases, the classic fluid-filled blisters might only appear during the baby’s first week of life ^[3].

Where Do They Appear?

HSV blisters can appear anywhere on a baby’s body. There is no single location that confirms or rules out the virus. Commonly involved areas include:

• The face, nose, and mouth ^[7][1].
• The scalp, especially at sites of minor trauma from delivery (such as from fetal scalp monitors) ^[8].
• The trunk and neck ^[9][1].

Eye Involvement

HSV can also infect the eyes, causing keratitis (an infection or inflammation of the clear front surface of the eye) ^[10][1]. This can threaten vision and requires urgent specialist care. Any new eye redness, swelling, excessive tearing, apparent light sensitivity, or discharge in a newborn should prompt immediate medical assessment, even if there are no visible blisters on the skin nearby.

Important Warning: Severe HSV Without Blisters

It is vital to know that a newborn can have a severe, life-threatening HSV infection without any visible skin, eye, or mouth sores. The virus can attack the central nervous system (the brain and spinal cord) or become disseminated (spread throughout the body to internal organs) without ever causing a rash ^[11]. In one major surveillance study, nearly 74% of infants diagnosed with disseminated HSV infection had no blisters or skin lesions at the time they presented to the hospital ^[8].

Never wait for a blister to appear if your baby seems unwell. Seek emergency medical care immediately if your newborn has any of the following warning signs:

• Fever or Low Temperature: A rectal temperature of 100.4°F (38.0°C) or higher, or an unusually low or unstable temperature, is a medical emergency in a newborn ^[8].
• Extreme sleepiness (lethargy) or refusing to feed ^[11].
• Unusual, constant irritability ^[11].
• Breathing difficulties ^[11].
• Seizures or abnormal movements ^[11].

Hospital Evaluation and Treatment

If your care team suspects HSV, they will likely run several tests. This usually involves swabbing the skin lesions, mouth, and eyes, drawing blood, and performing a lumbar puncture (spinal tap) to check the cerebrospinal fluid for brain involvement. Because neonatal HSV moves quickly, doctors will often start intravenous (IV) antiviral medication (like acyclovir) immediately while waiting for the test results to come back. The clinical team will decide exactly which tests and treatments are necessary based on your baby’s specific situation.