Cold sores are small fluid-filled blisters that typically develop on and around the lips. After the blisters break, a crust forms over the resulting sore. Cold sores usually heal in two to four weeks without leaving a scar. Although there is no cure, treatment with certain medications can help cold sores heal more quickly.
Cold sores are caused by certain strains of the herpes simplex virus (HSV). HSV type-1 is the strain that usually causes cold sores and is closely related to HSV type-2, which is the strain that usually causes genital herpes. However, either strain of HSV can cause blisters on and around the mouth or on the genitals.
They are most contagious when fluid is seeping from the blisters, but the virus can be transmitted to another person even when the blisters are too small to see. Transmission occurs through close contact, including kissing and sharing of eating utensils, razors, and towels. Also, oral sex can spread HSV type-1 to the genitals and HSV type-2 to the lips.
Most people are first exposed to the virus at a young age after close contact with a person who has a cold sore. The infection is permanent. Following the first episode of herpes infection, the virus lies inactive (dormant) inside nerves in the skin. It causes no symptoms most of the time but in some people the virus is periodically reactivated, and a cold sore re-emerges.
Cold sore recurrences can be triggered by:
- Viral infection or fever (which is why cold sores are also known as ‘fever blisters’)
- Anxiety or stress
- Fatigue/physical exhaustion
- Exposure to sunlight and/or wind
- Hormonal changes, such as those related to menstruation
- Changes in the immune system.
Cold sores tend to appear in the same place every time because the virus lies dormant in the nerves that lead to that spot on the skin.
The cold sore-causing HSV can cause problems in areas of the body other than the mouth, including:
- Fingertips: HSV can be spread to the fingers. For example, children who suck their thumbs may transfer the infection from their mouths to their thumbs
- Eyes: HSV can cause eye infections. Repeated eye infections can lead to scarring and injury, and possibly vision problems or blindness
- Widespread areas of skin: People with eczema , which is an inflammatory skin condition, are at higher risk of cold sores spreading over their bodies
- Other organs: In people with weakened immune systems, HSV can also affect the spinal cord, brain, and other organs.
People who have weakened immune systems due to other medical conditions or medical treatments are at higher risk of complications from HSV. Medical conditions and treatments that increase the risk of complications include:
- Severe burns
- Cancer chemotherapy
- Drugs used to prevent rejection of organ transplants.
Signs and symptoms
Cold sore signs and symptoms vary depending on whether it is a first outbreak or a recurrence, and typically can last several days. The blisters can take two to four weeks to heal completely. The signs and symptoms of cold sore recurrences tend to be less severe than the initial outbreak.
A cold sore episode usually passes through several symptom stages during a two- or three-day period:
- Burning or tingling and itching around the lips for a day or so before blisters appear
- Small fluid-filled blisters breakout along the border where the edge of the lips meets the skin of the face. Less commonly, cold sores occur around the nose or on the cheeks
- The blisters burst, leaving shallow open sores that ooze fluid and then crust over into a scab.
A first-time episode may be accompanied by fever, painful gums, sore throat, headache, muscle aches, and/or swollen lymph nodes.
Your GP can usually diagnose cold sores by looking at them. They may take a sample from the blister for testing in a laboratory to confirm the diagnosis.
Although cold sores generally clear up without treatment, several types of prescription or pharmacy-only antiviral drugs may speed the healing process.
Topical antiviral creams are available from pharmacies. They must be applied to the cold sore several times per day and work best if they are applied as soon as you recognise the early tingling feeling.
Oral antiviral medications in tablet form are available on prescription. In general, the tablets work better than the creams. Antiviral tablets are typically prescribed when a cold sore is very large, painful, or keeps coming back. For particularly severe infections, some antiviral drugs can be given with an injection.
The following home remedies may help to reduce the discomfort of a cold sore:
- Applying over-the-counter topical preparations that contain a drying agent, such as alcohol, may speed healing
- Applying a moisturising cream to soothe lips that have become dry
- Applying ice at the first sign of tingling may help shorten the duration of the sore or prevent it from becoming a full-blown cold sore
- Applying over-the-counter pain-relieving creams, such as those containing lidocaine or benzocaine, may provide some pain relief.
You should see a GP if a cold sore hasn't started to heal within 10 days, the cold sore is very large or painful, you or your child also have swollen, painful gums and sores in the mouth, you're pregnant, or you have a weakened immune system.
A pharmacist can recommend creams to ease pain and irritation, antiviral creams to speed up healing time, and cold sore patches to protect the skin while it heals.
An antiviral medication to be taken on a regular basis may be prescribed for people who get frequent recurrences of cold sores or who are at high risk of complications.
If sunlight seems to trigger recurrences, regular application of lip balms containing sunblock or zinc oxide cream to protect your lips from the sun may help to prevent an outbreak.
When you have cold sore blisters, taking the following precautions may help prevent spreading cold sores to other people or to other parts of your body:
- Avoiding skin-to-skin contact with others, especially kissing someone or having oral sex
- Avoiding sharing items such as cutlery, towels, lipstick or lip balm, which can spread the virus when blisters are present
- Avoiding kissing babies if you have a cold sore as it can lead to neonatal herpes, which is a serious condition in new-born babies
- Avoiding touching a cold sore unless applying cream
- Washing your hands with soap and water before and after applying cream and before touching other parts of your body or other people, especially babies.
If your cold sores are triggered by stress, relaxation techniques, such as deep-breathing exercises and meditation, may help to reduce recurrences.
Harvard Health Publishing (2015). Cold sores. Boston, MA: Harvard Medical School of Harvard University. https://www.health.harvard.edu/oral-health/cold-sores [Accessed 13/10/18]
Mayo Clinic (2018). Cold sore (Web Page). Rochester, NY: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/cold-sore/symptoms-causes/syc-20371017 [Accessed: 12/10/18]
NHS (2017). Cold sores (Web Page). Redditch: National Health Service (NHS)
England. https://www.nhs.uk/conditions/cold-sores/ [Accessed: 12/10/18]
NHS inform (2018). Cold sore (Web Page). Glasgow: National Health Information Service, National Health Service (NHS) Scotland. https://www.nhsinform.scot/illnesses-and-conditions/mouth/cold-sore [12/10/18]
Created: October 2018