Cold Sores

1 Cold Sores Summary

A cold sore is a skin lesion (abnormal feature on the skin) caused by infection of Herpes simplex virus-1 (HSV1). The medical term for cold sores is herpes labialis.


Cold sores are highly contagious, especially when an outbreak is present. Sharing eating utensils, towels, and activities like kissing and oral sex can spread cold sores. There is still no cure for cold sores, and individuals who have it will experience repeated appearance and resolution of lesions throughout life.

Cold sores are very common. Also, not all individuals infected with HSV1 exhibit symptoms of cold sores. It is estimated that around 40% of adults are infected with HSV1, and only around 25% exhibit cold sores. Cold sores can appear at any age and affect both sexes,

Epidemiological studies show that women tend to be at a higher risk of cold sores. Significant risk factors include engaging in sex before reaching 15 years of age, greater total years of sexual activity, having a partner with cold sores, and having a history of sexually-transmitted diseases.

HSV1 is usually the causative agent of cold sores. HSV1 is a close relative of Herpes simplex virus-2 (HSV2), which causes genital warts.

Herpes simplex-1 resides in the nerve cells, especially those under the skin. From time to time, HSV1 becomes active and forms cold sores. Cold sores disappear as the body creates antibodies that inactivate the virus, causing the skin to heal.

However, the body’s immune system is only capable of inactivating HSV1, so cold sores breaks out again after some time. This explains why cold sores recur again and again. The frequency of cold sore outbreaks tends to vary among patients.

Cold sores usually have triggers, which can differ among patients. Stress, menses, illnesses, fever, colds, allergies and having sunburn are common triggers. Having weak immune system can also cause cold sores to break out.

Cold sores is a sexually-transmitted disease because it can be spread to others via oral sex. Kissing can spread HSV-1 virus to others. Receiving oral sex from a person with cold sores can cause the appearance of cold sores in the genitals. Conversely, a person who performs oral sex to someone with HSV-2 infection or genital warts can have warts in the mouth area.

Cold sores are groups of tiny fluid-filled blisters that are often painful. These blisters burst within days and result to open sores, which heals on its own within two weeks without forming scars.

Cold sores often appear on or around the lips, but they can appear on the chin, cheeks, inside the nostrils, or less frequently on the gums or roof of the mouth (palate). Cold sores can also appear on the genitals, cornea of the eyes (called herpetic keratitis) and fingertips (called herpetic willow).

Typically, cold sores appear and disappear, although some patients remain infected but do not have outbreaks of lesions.

Cold sores are easily diagnosed by doctors. Treatments include administration of antiviral medications. Note that medicines will only work to reduce the severity of cold sores, but it does not cure it.

2 Causes

Herpes simplex virus-1 (HSV1) is the only cause of cold sores. HSV1 is a virus that infects and replicates inside the cells. In the case of HSV1, it infects and resides in nerve cells (neurons).

HSV1 is highly transmissible, and it spreads to others via skin-to-skin contact. A person infected with HSV1 can transmit the virus to others, whether cold sores are present or not. However, HSV1 is highly transmissible if cold sores are present and if the sores are oozing.

Cold sores are highly contagious. Cold sores are primarily spread to others by sex, notably oral sex. Oral sex can cause cold sores on the genitals or on other parts of the body. Touching blisters, kissing, sharing towels, toothbrushes, shaving instruments, and eating utensils can also spread HSV1 to others. There is also evidence that HSV1 can be present in saliva, semen, and vaginal fluids.

Although rare, cold sores can be spread to other parts of the body. This explains why some patients have cold sores on the eyes, fingertips, anus, or the genitals. This is uncommon because the body usually develops antibodies against the virus.

Note that cold sores cannot be spread via respiratory droplets (sneezing, coughing) or contact with blood from someone with cold sores.

Also, note that herpes simplex 2 (HSV2), which cause genital herpes, can also infect and form sores in the mouth area that can be mistaken for cold sores.

In patients with cold sores, outbreaks usually occur after certain triggers. These triggers activate the virus that results to outbreaks of cold sores. The most common triggers include stress, sunburn, illnesses, having menses, fever, allergies, and trauma to the mouth area.

3 Diagnosis & Treatment


Cold sores are small fluid-filled blisters surrounded by reddish or inflamed skin. Cold sores occur in small groups and are often itchy or painful. In a few days' time, the blisters burst to leave open sores that heal on their own without leaving scars. Before cold sores appear, the affected area may first tingle or burn slightly. The initial outbreak of cold sores is usually severe, and subsequent outbreaks are usually milder and shorter in duration especially if treated accordingly.

If you are experiencing an outbreak, the doctor can easily diagnose it by simply looking at it.

There are other tests used in diagnosing cold sores and determining whether it is caused by HSV1 or HSV2. In herpes viral culture procedure, the doctor will get a sample of fluid from the blister and have it examined for the presence of HSV1 viruses, which confirms the diagnosis. In herpes virus antigen detection test, sample tissue from the sore is tested for antigens or markers of HSV1. PCR (polymerase chain reaction test) checks for DNA of HSV1 in the blood or spinal fluid.

A sample of your blood can also be examined for the presence of antibodies to HSV1, which can indicate exposure to the virus but does not indicate the presence of active infection.


Treatment for cold sores speeds up clearing and healing of cold sore outbreaks. Although cold sores heal on their own, treatments relieve symptoms and shorten the duration of appearance of cold sores. Prescription antiviral drugs, which stops the virus from replicating, is effective for cold sores. These antivirals also relieve pain, itching, burning or tingling sensation. Since antivirals slow reproduction of the virus, it reduces the contagiousness of cold sores as well.

Most frequently prescribed antivirals include Acyclovir, Famciclovir, Penciclovir, and Valacyclovir. These are available as pills, skin creams or can be injected by the doctor. Injected antivirals are usually reserved for severe outbreaks.
You can also apply cold compresses onto cold sores to relieve pain. Skin creams with Docosanol, or alcohol, speed up drying and healing of cold sores. Lidocaine or benzocaine skin creams relieve pain and tingling, while lip balms with sunblock or zinc oxide protect the skin from irritation.

4 Related Clinical Trials