Cold sores are sometimes called oral herpes because they are caused by the herpes simplex virus type 1 (HSV-1). Cold sores are most contagious when you have oozing blisters because the virus easily spreads through contact with infected body fluids. But you can spread the virus even if you don’t have blisters. Many people who are infected with the virus that causes cold sores never develop signs and symptoms.
What triggers a cold sore?
Once you’ve had an episode of herpes infection, the virus lies dormant in nerve cells in your skin and may emerge as another cold sore at the same place as before. What triggers a cold sore in one person might not cause an outbreak in another person. Some people with HSV-1 never develop a cold sore.
A cold sore can be activated by a variety of factors, including:
- Hormonal changes during menstruation or pregnancy
- Sunburn
- Extreme temperatures (hot or cold)
- Stress (physical or emotional)
- Fatigue
- Fever and illness, such as cold or flu
- Damaged, dry or cracked lips
- Viral infection or fever
- Injury to the skin, such as a cut, to the area where you have had cold sores
- Some foods
- Allergies
- Dental work or cosmetic surgery
- Alcohol
Risk factors
Almost everyone is at risk of cold sores. Most adults carry the virus that causes cold sores, even if they’ve never had symptoms. You’re most at risk of complications from the virus if you have a weakened immune system from conditions and treatments such as:
- HIV/AIDS
- Atopic dermatitis (eczema)
- Cancer chemotherapy
- Anti-rejection drugs for organ transplants
While cold sores are highly contagious, they usually aren’t serious. In healthy people, cold sores generally clear up on their own in one to two weeks. You may need to see a doctor if you have more severe symptoms or a weakened immune system — if, for example, you have HIV or you are having cancer treatment. It’s also a good idea to see your doctor if:
- there are signs the cold sore is infected, such as redness around the sore, pus and a fever
- you aren’t sure you have a cold sore
- the cold sore isn’t healing, it’s spreading or you have more than one cold sore
- your cold sore has spread to near your eyes
- you get cold sores often