Cold sores are painful, contagious blisters around the mouth and on the lips. They are caused by herpes simplex virus (HSV) infection.

There are two types of HSV: HSV-1 and HSV-2. HSV infection can manifest in many different ways and is frequently asymptomatic (i.e., without symptoms).^[1][2] After the initial infection, HSV goes dormant, but it remains in the body. In some people with HSV, the virus periodically reactivates and causes cold sore outbreaks, which are known as “recurrences,” in roughly the same place as the initial infection.^[3] Cold sores are most often due to HSV-1 infection but can also be due to HSV-2.^[1][2]

Cold sores are often preceded by a tingling or burning sensation. The sores start as painful clustered blisters on a red, swollen base. They primarily occur on or around the lips and mouth (“herpes labialis”) but can also occur elsewhere on the face. Once a blister has appeared, it generally lasts from 24 to 48 hours before ulcerating and forming a crust. The crusting may remain for 5 to 7 days, but it generally heals without scarring. Complete healing may take 7 to 10 days. A cold sore recurrence (outbreak) in a person with a fully functioning immune system will normally resolve on its own, although treatment can shorten the length of the outbreak, speed up healing, and reduce viral shedding. Untreated lesions in immunosuppressed people can last for weeks or months.^{[4][3][1][2][5][6][7]}

Cold sore stages (adapted from Semprini 2019^[8]):

Suspected cold sores should be diagnosed by a clinician in order to differentiate between herpes simplex virus (HSV) and other causes of oral sores. Cold sores are often diagnosed by visual inspection, but lab tests can also be performed, including viral culture and/or polymerase chain reaction (PCR) testing of a fresh swab taken from the active sore. Blood tests for HSV antibodies can be done but aren’t as useful for diagnosis, because being HSV-positive doesn’t mean a person will get cold sores. Many people with HSV antibodies will never get cold sores.^[4][3]

There is no cure for the herpes simplex virus (HSV) infection that causes cold sores, but treatment with oral and/or topical (applied to the skin) antiviral medication at the first sign of an outbreak can reduce the outbreak’s duration, speed healing, and reduce the amount of viral shedding. Oral antivirals, such as valacyclovir, are more effective than topical antivirals.^[9][1][4] In people who have frequent outbreaks or are immunocompromised, oral antivirals are sometimes taken long-term to reduce the frequency of outbreaks.^[1][2][10] Because UV exposure is known to trigger outbreaks, sunscreen is sometimes recommended as a preventative. However, while there is evidence that sunscreen may reduce the risk of outbreaks triggered by artificial (experimental) UV exposure, that evidence is very low quality, and there is even some low-quality evidence that sunscreen might slightly increase the risk of outbreaks triggered by sunlight exposure.^[10]

Several supplements have been studied for cold sores, including lemon balm and honey. Some studies compare the treatment to a placebo ointment, gel, or cream with no active ingredients. Others compare the treatment to topical (on the skin) antiviral cream. With the latter studies, it’s worth remembering that topical antiviral cream isn’t the standard of medical care, because prescription oral antivirals are more effective. In other words, just because a supplement is better than a placebo or as good as antiviral cream doesn’t mean it’s the best treatment: An oral antiviral may be more effective. Unfortunately, no studies have compared supplements to oral antiviral medication.

A cream containing 1% dried lemon balm extract has been tested to treat oral or genital herpes sores and appears to be moderately effective compared to a placebo at reducing the severity of symptoms on the second day.^[11][12] Little research has directly compared lemon balm to prescription antivirals; one randomized controlled trial (RCT) found that lemon balm cream reduced symptoms on the second day more than topical acyclovir (an antiviral) but was otherwise comparable.^[13] Prescription oral antivirals are likely more effective.

Honey and propolis have also been studied for cold sores.^[14] In a meta-analysis of three different RCTs comparing 0.5%–3% propolis ointment to acyclovir cream, the participants who used propolis were more likely to be completely healed by the 7th day of an outbreak than the participants who used acyclovir.^[15] And in a meta-analysis of three RCTs comparing honey to acyclovir cream, honey healed cold sores faster than acyclovir cream, with an equivalent reduction in pain to acyclovir cream, although there was quite a lot of variability between the three studies and one of them had a high risk of bias.^[15] Again, because prescription oral antivirals are superior to topical acyclovir, they’re likely more effective than honey. More research needs to be done to determine how propolis cream would compare to prescription antiviral medicine.

Prompt treatment with zinc oxide or zinc sulfate cream, or an anesthetic cream, can slightly reduce the duration of symptoms.^[16] When used alongside oral antiviral treatment, cold sore symptoms can be managed with topical (on the skin) analgesics (i.e., pain relievers), like over-the-counter, lidocaine-containing oral sprays and mouthwashes, although these shouldn’t be used in children before meals because of the risk of choking. Proper hydration and nutrition are also important to help healing. It’s particularly important to make sure that children eat and drink enough during an outbreak, despite the painful lesions.^[5]

Low-level laser therapy for herpes simplex virus (HSV) sores does seem to be effective at speeding healing by about 1 day, although higher-quality clinical trials are needed to confirm this.^[17] It does not seem to be effective at preventing recurrences.^[10]

Finally, hypnotherapy and local concentrated heat (LCH) have been investigated as treatments for cold sores, but much more research is needed. LCH can be briefly applied to the affected area at the first sign of an outbreak (itching, tingling), but much more research is needed to establish whether or not this is effective. A single 2013 pilot study found that LCH was more effective than topical antiviral cream at reducing the severity of burning, itching and tingling on days 2–7 of an outbreak, but these results are preliminary, and more research is needed.^[18] Hypnotherapy has also been briefly investigated: A single, small 1984 study found that hypnotherapy reduced the severity and recurrence rate of cold sore outbreaks, but the quality of this evidence is very low, and more research is needed.^[10][19]

The herpes simplex virus (HSV) infection that causes cold sores can be spread by direct contact with cold sores or by exposure to an infected person’s saliva, such as by kissing or by sharing towels, drinking glasses, utensils, makeup, etc.^[1][6] Most infections occur after exposure to the saliva or sores of someone with an active, symptomatic infection, although asymptomatic transmission can occur.^[6] People with active sores can also spread the virus to previously unaffected parts of the body, so handwashing is important during an active cold sore outbreak.