Eight types of herpesvirus infect humans, numbered HHV-1 through HHV-8. Most people are familiar with only one or two of them, but every type establishes a lifelong infection once contracted, hiding in specific cells and occasionally reactivating. When scientists split HHV-6 into two distinct species (6A and 6B), the functional count rose to nine. Beyond humans, the herpesvirus family includes over 100 species that infect animals ranging from birds to reptiles.
The Two Most Recognized: HSV-1 and HSV-2
Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are what most people mean when they say “herpes.” HSV-1 mostly spreads through oral contact and causes cold sores in or around the mouth, though it can also cause genital herpes through oral-genital contact. HSV-2 spreads through sexual contact and primarily causes genital herpes. Both can be transmitted even when no visible sores are present.
Symptoms, when they appear, often start with tingling, itching, or burning before blisters or open sores develop. A first outbreak may come with fever, body aches, headache, and swollen lymph nodes. Recurrences happen over time but tend to be shorter and less severe than the initial episode. Many people carry one or both viruses without ever showing symptoms.
Varicella-Zoster Virus (HHV-3)
This is the virus behind two familiar illnesses: chickenpox and shingles. Primary infection, usually in childhood, causes chickenpox. After recovery, the virus retreats into nerve cells in clusters called ganglia along the spine and near the base of the skull. It can stay dormant for decades before reactivating as shingles, a painful rash that typically appears in a band on one side of the body. Reactivation can also lead to serious neurological complications, including inflammation of the brain, spinal cord, or blood vessels.
Epstein-Barr Virus (HHV-4)
Epstein-Barr virus is best known as the cause of infectious mononucleosis, or “mono,” the prolonged fatigue illness common in teenagers and young adults. But it is also linked to several cancers. Early childhood infection tends to be mild or silent, while infection later in life is more likely to trigger mono. Over a lifetime, the virus’s ability to linger in immune cells can contribute to nasopharyngeal cancer, Burkitt lymphoma, Hodgkin lymphoma, and certain stomach cancers. Rarer associations include some breast, thyroid, and liver cancers.
Cytomegalovirus (HHV-5)
Cytomegalovirus, or CMV, is extremely common and usually harmless in healthy adults. It becomes dangerous in two specific situations: when a baby is infected before birth, and when someone has a weakened immune system.
About 1 in 200 babies is born with congenital CMV infection. Of those, roughly 1 in 5 will develop birth defects or long-term health problems. Hearing loss is the most common, sometimes appearing at birth and sometimes developing later in childhood. Brain, liver, spleen, lung, and growth problems can also occur. In people with compromised immunity, such as organ transplant recipients or those with advanced HIV, CMV can cause serious disease affecting the eyes, lungs, liver, and digestive tract.
The Roseolaviruses: HHV-6A, HHV-6B, and HHV-7
These three viruses are so widespread that nearly everyone contracts them by early childhood. HHV-6B and HHV-7 both cause roseola infantum, the classic toddler illness marked by several days of high fever followed by a pinkish rash lasting one to four days. The two viruses produce symptoms so similar they are clinically indistinguishable. HHV-6A, by contrast, typically causes no symptoms at all in young children.
Adult seroprevalence tells the story of how universal these infections are: 80 to 96% of adults carry HHV-6B, and 75 to 98% carry HHV-7. Primary HHV-7 infection tends to happen slightly later than HHV-6B, with about 75% of children testing positive by age 5. Most infections pass uneventfully, but neurological complications including seizures and, in rare cases, encephalitis can occur. Reactivation later in life has been linked to conditions including multiple sclerosis (for HHV-6A) and heart inflammation (for HHV-7), though these associations are still being studied.
Because HHV-6A and HHV-6B are now classified as separate species, some diagnostic tools count nine human herpesviruses rather than eight.
Kaposi Sarcoma-Associated Herpesvirus (HHV-8)
HHV-8 is the least common of the human herpesviruses and the most recently discovered, identified in the 1990s. It causes all forms of Kaposi sarcoma, a cancer that produces dark skin lesions and can affect internal organs. This includes the “epidemic” form seen in people with advanced HIV, as well as forms that appear after organ transplantation or in certain geographic regions where the virus is endemic.
Beyond Kaposi sarcoma, HHV-8 is responsible for primary effusion lymphoma and a lymph node disorder called multicentric Castleman’s disease. Transmission appears to occur primarily through saliva, though genital secretions and, in some regions, blood transfusion and mother-to-child transmission during birth are also routes. In most healthy people who contract it, HHV-8 causes no noticeable illness. Serious disease develops almost exclusively in those with suppressed immune systems.
How All Herpesviruses Share a Common Trait
The defining feature of every herpesvirus is latency. After the initial infection clears, the virus does not leave the body. Instead, it inserts its genetic material into specific host cells and goes quiet, sometimes for years or an entire lifetime. HSV-1, HSV-2, and varicella-zoster hide in nerve cells. EBV and HHV-8 persist in immune cells. CMV lingers in blood cell precursors and various tissues.
This means that all eight (or nine) human herpesviruses are, in a real sense, permanent. The immune system keeps them in check, but it cannot eliminate them. When immunity weakens due to stress, aging, illness, or medication, any of these viruses can reactivate and cause symptoms again. That shared biology is why herpesviruses, despite causing such different diseases, belong to the same family.