What Causes Fever Blisters on Lips?

Fever blisters

Fever blisters, also known as cold sores, are painful and contagious lesions that typically appear on or around the lips. They are caused by the herpes simplex virus (HSV), specifically HSV-1. Here’s how fever blisters on the lips develop:

  • Initial Infection: The initial infection with HSV-1 often occurs during childhood or adolescence. It can manifest as a mild, flu-like illness or as an asymptomatic infection. Once the virus enters the body, it remains dormant (inactive) in the nerve cells of the face, specifically the trigeminal ganglion.
  • Reactivation: Periodically, the dormant HSV-1 virus can reactivate and travel back to the surface of the skin, often near the lips. This reactivation can be triggered by various factors, including:
    • Stress: Emotional stress or physical stressors can weaken the immune system, making reactivation more likely.
    • Fever or Illness: As the name “fever blister” suggests, fever and illnesses that weaken the immune system can trigger outbreaks.
    • Sunlight: Overexposure to sunlight, particularly on the lips, can trigger an outbreak.
    • Hormonal Changes: Hormonal fluctuations, such as those that occur during menstruation, can also lead to reactivation.
  • Fever Blister Formation: Once reactivated, the virus multiplies and moves to the skin’s surface. This leads to the development of a blister or cluster of small, painful fluid-filled sores on or around the lips. The blisters are often surrounded by redness and inflammation.
  • Rupture and Crusting: The blisters eventually rupture, releasing the infectious fluid. The sores then crust over as they begin to heal.
  • Contagiousness: Fever blisters are highly contagious during the active phase when they are oozing fluid. Close contact, such as kissing or sharing utensils, can transmit the virus to others.

It’s important to note that while HSV-1 is the primary cause of fever blisters on or around the lips, a closely related virus called HSV-2 can also cause oral herpes infections, although it is more commonly associated with genital herpes.

Fever blisters typically resolve on their own within 7 to 10 days. Antiviral medications may be prescribed by a healthcare provider to help reduce the severity and duration of an outbreak, especially if the outbreaks are frequent or particularly painful.

To reduce the risk of spreading the virus or experiencing recurrent outbreaks, individuals with fever blisters should avoid close contact with others during active outbreaks, practice good hand hygiene, and refrain from sharing items that come into contact with the mouth, such as utensils or lip balm. Additionally, individuals with frequent or severe outbreaks may benefit from discussing long-term antiviral suppression therapy with their healthcare provider.

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