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Herpes Simplex Virus (HSV) Infections


Kenneth M. Kaye

, MD, Harvard Medical School

Reviewed/Revised Dec 2023
Topic Resources

Herpes simplex virus infection causes recurring episodes of small, painful, fluid-filled blisters on the skin, mouth, lips (cold sores), eyes, or genitals.

HSV is very contagious and can be spread by direct contact with sores and sometimes by contact with the mouth (oral area) or genitals of people who have HSV infection even when no sores are can be seen.

Primary and recurrent (reactivated) infection

After the first (primary) infection, HSV, like other herpesviruses, remains inactive (dormant or latent) in the body for life. A latent infection may not cause symptoms again, or it may periodically reactivate and cause symptoms.

The primary HSV infection produces an eruption of tiny blisters. After the eruption of blisters subsides, the virus remains in a dormant state inside the collection of nerve cells (ganglia) near the spinal cord that supply the nerve fibers to the infected area. Periodically, the virus reactivates, begins multiplying again, and travels through the nerve fibers back to the skin—causing eruptions of blisters in the same area of skin as the earlier infection. Sometimes the virus is present on the skin or mucous membranes even when no blisters can be seen.

The virus may reactivate many times. Reactivation of a latent oral or genital HSV infection may be triggered by the following:

Often, the trigger is unknown.

Symptoms and Complications of HSV Infections

Tiny blisters appear on the following:

  • Skin: Particularly around the mouth or on the genitals

  • Mucous membranes: Including those lining the eyes, vagina, cervix, or inside of the mouth.

The skin around the blisters is often red.

Oral infection

The first oral infection with HSV usually causes many painful sores inside the mouth (herpetic gingivostomatitis). Herpetic gingivostomatitis most commonly develops in children.

People usually feel sick and have a fever, a headache, and body aches.

The mouth sores last 10 to 19 days and are often very severe, making eating and drinking extremely uncomfortable. As a result, people may become dehydrated. Occasionally, no symptoms develop.

Recurrences usually produce a cluster of sores on the rim of the lip.

The lip sore is called a cold sore or fever blister (so named because they are often triggered by colds or fevers). Other triggers include over-exposure to sun on the lips, anxiety, certain dental procedures, and any condition that reduces the body's resistance to infection.

Before a cold sore appears, people usually feel a tingling at the site, lasting from minutes to a few hours, followed by redness and swelling. Usually, fluid-filled blisters form and break open, leaving sores. The sores quickly form a scab. After about 5 to 10 days, the scab falls off and the episode ends. Less often, tingling and redness occur without blister formation.

Other infections and complications

Genital herpes Genital Herpes Genital herpes is a sexually transmitted infection caused by the herpes simplex virus that causes recurring episodes of small, painful, fluid-filled blisters on and around the genitals. This... read more Genital Herpes causes painful blisters in the genital and/or anal area. In women, internal blisters may develop in the vagina or on the cervix. Internal blisters are less painful and are not visible. The blisters develop 4 to 7 days after people are infected. The blisters go away but may come back (recur) because the virus never truly leaves the body. Blisters caused by a first genital infection are usually more painful, last longer, and are more widespread than those caused by a recurrent infection.

In people with a weakened immune system, recurrences of oral or genital herpes can result in progressive, gradually enlarging sores that take weeks to heal. The infection may progress inside the body, moving into the esophagus, lungs, or colon. Ulcers in the esophagus cause pain during swallowing, and lung infection causes pneumonia with cough and shortness of breath.

Sometimes HSV-1 or HSV-2 enters through a break in the skin of a finger, causing a swollen, painful, red fingertip (herpetic whitlow Herpetic Whitlow Herpetic whitlow is a viral infection of the fingertip. (See also Overview of Hand Disorders.) Herpes simplex virus (similar to the one that causes fever blisters) may cause an intense, painful... read more Herpetic Whitlow ). Health care workers who are exposed to saliva or other body secretions (such as dentists) when not wearing gloves are most commonly affected.

HSV-1 can infect the cornea of the eye. This infection (called herpes simplex keratitis Herpes Simplex Keratitis Herpes simplex keratitis is an eye infection that involves the cornea (the clear layer in front of the iris and pupil) and is caused by herpes simplex virus. The infection commonly recurs and... read more Herpes Simplex Keratitis ) causes a painful sore, tearing, sensitivity to light, and blurred vision. Over time, particularly without treatment, the cornea can become cloudy, causing a significant loss of vision.

Infants or adults with a skin disorder called atopic eczema Atopic Dermatitis (Eczema) Atopic dermatitis (commonly referred to as eczema) is chronic, itchy inflammation of the upper layers of the skin that often develops in people who have hay fever or asthma and in people who... read more Atopic Dermatitis (Eczema) can develop a potentially severe HSV infection in the area of skin that has the eczema (eczema herpeticum). Therefore, people with atopic eczema should avoid being near anyone with an active herpes infection.

Infrequently, a pregnant woman can transmit HSV infection to her baby (called neonatal herpes Herpes Simplex Virus (HSV) Infection in Newborns Herpes simplex virus infection usually causes only annoying, recurring blisters in healthy adults but can cause severe infection in newborns. Newborns may become infected at birth or after birth... read more Herpes Simplex Virus (HSV) Infection in Newborns ). Transmission usually occurs at birth, when the baby comes into contact with infected secretions in the birth canal. Rarely, HSV is transmitted to the fetus during pregnancy. Transmission during birth is more likely when

  • The mother has recently acquired the herpes infection

  • The mother has visible herpes sores in the vaginal area, although babies may become infected from mothers who have no apparent sores

When acquired at birth, the infection appears between the first and fourth week of life. Newborns with HSV infection become very ill. They may have widespread disease, brain infection, or skin infection. Without treatment, about 85% of those with widespread disease and about half of those with a brain infection die. Even with treatment, many have brain damage.

Diagnosis of HSV Infections

  • Testing of a sample taken from the sore

  • If doctors suspect a brain infection, magnetic resonance imaging and a spinal tap

Herpes simplex virus infection is usually easy for doctors to recognize. If unsure, doctors may use a swab to take a sample of material from the sore and send the swab to a laboratory to grow (culture) and identify the virus.

Material from the sore can also be tested using polymerase chain reaction (PCR) to identify the herpes simplex DNA. PCR is a more sensitive test than viral culture, which means it will miss fewer cases of the virus.

Sometimes doctors examine material scraped from the blisters under a microscope. Although the virus itself cannot be seen, scrapings sometimes contain enlarged infected cells (giant cells) that are characteristic of infection by a herpes-type virus.

Blood tests to identify antibodies to HSV can also be helpful. (Antibodies Antibodies One of the body's lines of defense ( immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more Antibodies are produced by the immune system to help defend the body against a particular attacker, such as HSV.)

Certain blood tests can distinguish between HSV-1 infection and HSV-2 infection.

Treatment of HSV Infections

Antiviral medications

No current antiviral treatments can eradicate HSV infection, and treatment of a first oral or genital infection does not prevent chronic infection of nerves. However, during recurrences, antiviral medications such as acyclovir, valacyclovir, or famciclovir, may relieve discomfort slightly and help symptoms resolve a day or two sooner (see table Some Antiviral Medications for Herpesvirus Infections Some Antiviral Drugs for Herpesvirus Infections Some Antiviral Drugs for Herpesvirus Infections ). Treatment is most effective if started early, usually within a few hours after symptoms start—preferably at the first sign of tingling or discomfort, before blisters appear. For people who have frequent, painful attacks, the number of outbreaks can be reduced by taking antivirals every day indefinitely (called suppressive therapy). However, taking antivirals does not necessarily prevent infected people from transmitting the infection. Most antivirals are available by prescription only.

Penciclovir cream, applied every 2 hours during waking hours, can shorten the healing time and duration of symptoms of a cold sore by about a day. Nonprescription creams containing docosanol (applied 5 times a day) may provide some relief. Acyclovir, valacyclovir, or famciclovir taken by mouth for up to a few days may be the most effective treatment for recurring cold sores.

Other treatments

For people who have minimal discomfort, the only treatment needed for recurring herpes of the lips or genitals is to keep the infected area clean such as by gentle washing with soap and water. Applying ice may be soothing and reduce swelling.

Applying prescription or nonprescription topical anesthetics, such as benzocaine, may help relieve pain. If the mouth contains many sores, the mouth can be rinsed with lidocaine. These anesthetics should not be swallowed. Topical anesthetics should only be taken as directed. If taken more often than directed, these medications can have harmful side effects.

Pain relievers may be taken for pain.

Prevention of HSV Infections

People with HSV infection should avoid activities and other things known to trigger recurrences. For example, people with oral HSV infection triggered by sunlight should avoid exposure to sunlight as much as possible or use sunscreen when sunlight cannot be avoided.

Because HSV infection is contagious, people with infection of the lips should avoid kissing as soon as they feel the first tingling (or, if no tingling is felt, when a blister appears) until the sore has completely healed. They should not share a drinking glass and, if possible, should not touch their lips. They should also avoid oral sex.

People with genital herpes should use condoms Condoms Barrier contraceptives physically block the sperm’s access to a woman’s uterus. They include condoms, diaphragms, cervical caps, contraceptive gels, contraceptive sponges, and spermicides (foams... read more Condoms at all times. Even when there are no visible blisters and no symptoms, the virus may be present on the genitals and can be spread to sex partners.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Sitavig, Zovirax, Zovirax Cream, Zovirax Ointment, Zovirax Powder, Zovirax Suspension
Advocate Pain Relief Stick, Americaine, Anbesol, Anbesol Baby , Anbesol Jr , Banadyne-3, Benzodent, Benz-O-Sthetic, Boil-Ease, Cepacol Sensations, Chloraseptic, Comfort Caine , Dry Socket Remedy, Freez Eez, HURRICAINE, HURRICAINE ONE, Little Remedies for Teethers, Monistat Care, Orabase, OraCoat CankerMelts, Orajel, Orajel Baby, Orajel Denture Plus, Orajel Maximum Strength, Orajel P.M., Orajel Protective, Orajel Severe Pain, Orajel Swabs, Orajel Ultra, Oral Pain Relief , Oticaine , Otocain, Outgro, Pinnacaine, Pro-Caine, RE Benzotic, Topex, Topicale Xtra, Zilactin-B
7T Lido, Akten , ALOCANE, ANASTIA, AneCream, Anestacon, Aspercreme with Lidocaine, AsperFlex, Astero , BenGay, Blue Tube, Blue-Emu, CidalEaze, DermacinRx Lidocan III, DermacinRx Lidogel, DermacinRx Lidorex, DERMALID, Ela-Max, GEN7T, Glydo, Gold Bond, LidaFlex, LidaMantle, Lidocan, Lidocare, Lidoderm, LidoDose, LidoDose Pediatric, Lidofore, LidoHeal-90, LIDO-K , LidoLite, Lidomar , Lidomark, LidoPure, LidoReal-30, LidoRx, Lidosense 4 , Lidosense 5, Lidosol, Lidosol-50, LIDO-SORB, Lidotral, Lidovix L, LIDOZION, Lidozo, LMX 4, LMX 4 with Tegaderm, LMX 5, LTA, Lydexa, Moxicaine, Numbonex, ReadySharp Lidocaine, RectaSmoothe, RectiCare, Salonpas Lidocaine, Senatec, Solarcaine, SUN BURNT PLUS, Tranzarel, Xyliderm, Xylocaine, Xylocaine Dental, Xylocaine in Dextrose, Xylocaine MPF, Xylocaine Topical, Xylocaine Topical Jelly, Xylocaine Topical Solution, Xylocaine Viscous, Zilactin-L, Zingo, Zionodi, ZTlido
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