These complications are uncommon — most people with HSV-1 will never face them. But they are real, they can be severe, and some are life-threatening. Knowing the warning signs saves sight and lives.
Keep this in perspective
The complications below are the exception, not the rule. For most people HSV-1 never causes anything worse than a cold sore. The point of this page is not to frighten, but to make sure the rare serious outcomes are recognised early — because with several of them, fast treatment changes everything.
The serious complications
Life-threateningRare
Herpes simplex encephalitis (brain infection)
HSV-1 can, rarely, infect the brain and cause encephalitis — dangerous inflammation of brain tissue. It is one of the most serious things the virus can do: HSV is the most common cause of sporadic (non-epidemic) fatal encephalitis worldwide. Left untreated, mortality is as high as around 70%, and even with treatment many survivors are left with lasting effects such as memory problems, seizures or personality change.
The reason it's on every doctor's mind is that early antiviral treatment dramatically improves the odds. Warning signs include severe or unusual headache, fever, confusion or strange behaviour, difficulty speaking, seizures, and a stiff neck. This is a medical emergency — every hour matters.
Sight-threateningUncommon
Herpes keratitis (eye infection)
When HSV-1 infects the eye, it can cause herpes keratitis — infection of the cornea, the clear front surface of the eye. Repeated episodes can scar the cornea, and HSV eye disease is a leading infectious cause of corneal blindness, sometimes requiring a corneal transplant. Symptoms include a painful, red, watering eye, light sensitivity, blurred vision and a feeling of something in the eye. Prompt treatment by an eye specialist protects vision — never treat a suspected herpes eye infection with steroid drops on your own, as they can make it much worse.
Life-threateningRare
Neonatal herpes (infection in newborns)
Newborn babies have immature immune systems, so HSV can overwhelm them quickly. Neonatal herpes can spread to the brain and internal organs; without treatment, disseminated (widespread) disease has a mortality rate around 85%, and many survivors of severe disease have lasting neurological damage. A baby can catch it during birth or afterwards — including from a cold sore via a kiss. This is why no one with a cold sore should kiss a newborn, and why any blister, unusual rash, poor feeding, lethargy or fever in a newborn needs immediate medical assessment.
Can be severeUncommon
Eczema herpeticum
In people with eczema or other skin barrier conditions, HSV-1 can spread across broken skin to cause eczema herpeticum — a widespread, painful blistering infection that can make a person very unwell and occasionally becomes serious. It looks like clusters of small, punched-out sores over eczema-affected areas, often with fever. It needs prompt antiviral treatment.
Can be severeHigher-risk groups
Severe disease in immunocompromised people
For people whose immune systems are weakened — for example by HIV, cancer treatment, or organ-transplant medication — HSV-1 can cause more frequent, more extensive and longer-lasting outbreaks, and can spread to internal organs. The World Health Organization notes that in immunocompromised people, herpes produces more severe symptoms and more frequent recurrences. This group should seek medical advice promptly for any significant outbreak.
Localised
Herpetic whitlow (finger infection)
HSV-1 can infect a finger — classically through contact with a sore — causing herpetic whitlow: painful blisters and swelling on the finger or thumb. It is usually not dangerous but can be very painful and is easily mistaken for a bacterial infection.
What researchers are still studying
Scientists are actively investigating possible longer-term associations between HSV-1 and other conditions — including a debated link with a higher risk of Alzheimer's disease. It's important to be accurate here: this is an area of ongoing research, and a link seen in studies does not prove that HSV-1 causes these conditions. It is a reason for continued research, not a reason for alarm. We mention it because you may see it in the news, and it deserves honest, careful framing rather than hype.
Get emergency help for these
Brain: severe/unusual headache, fever, confusion, strange behaviour, trouble speaking, seizures or a stiff neck.
Eye: a painful red eye, light sensitivity or any sudden change in vision.
Newborn: any sore, blister, rash, fever, floppiness or poor feeding in a baby — treat as urgent.
Call your local emergency number or go to an emergency department. With encephalitis and neonatal herpes especially, early antiviral treatment saves lives.