A cold sore, also known as a fever blister, is a common viral infection characterized by the development of small, fluid-filled blisters or sores on or around the lips, although they can also appear on other areas of the face or inside the mouth.
Cold sores, sometimes called fever blisters, are small, painful, fluid-filled lesions that typically appear on or around the lips. They may also develop on the chin, cheeks, nose, or inside the mouth. These outbreaks are caused by a viral infection and tend to recur in cycles.
What Causes Cold Sores?
Cold sores are the result of infection with the herpes simplex virus (HSV)—most often HSV-1, although HSV-2 can also cause sores in some cases.
Once a person becomes infected, the virus settles into nearby nerve cells, where it can remain inactive for long periods. At various times, the virus may “reactivate,” leading to a new outbreak of cold sores. Several triggers can encourage reactivation, including:
Herpes Simplex Virus Infection
Cold sores spread easily through close contact, such as:
- Kissing
- Sharing drinks, utensils, or lip products
- Oral sexual contact
Because HSV is highly contagious, a person can contract the virus even when no visible sores are present.
Stress
Emotional or physical stress can weaken the immune system, making it easier for HSV to reactivate and cause a new flare-up.
Sunlight Exposure
Ultraviolet (UV) radiation, sunburn, or excessive sun exposure can trigger outbreaks in people prone to cold sores.
Illness or Fatigue
Viral infections (such as the common cold), fever, or general immune suppression may increase the chances of a recurrence.
Stages and Symptoms of Cold Sores
Cold sores typically follow a predictable sequence of stages:
- Tingling or Burning Sensation Many people feel itching, tingling, or warmth at the site where a sore will appear. This is often the first sign of an impending outbreak.
- Blister Formation Small clusters of clear, fluid-filled blisters appear on the skin or lips.
- Ulceration The blisters break open, leaving shallow open sores. This stage can be painful.
- Crusting The sores gradually dry out and form a yellowish or brown crust.
- Healing Within 7–10 days, the scab falls away and the skin heals, sometimes leaving temporary redness.
Important Considerations
Cold sores are contagious throughout the entire cycle, from the tingling stage until the area is fully healed. Outbreak frequency varies widely—some people experience recurrent episodes several times a year, while others may have only one outbreak in their lifetime.
Although there is no cure for HSV, antiviral medications can shorten outbreaks and reduce how often they occur. Individuals with frequent, severe, or persistent cold sores should speak with a healthcare provider for personalized treatment options.
