Cold sores, commonly referred to as fever blisters, are small, fluid-filled lesions that appear on or around the lips. They are caused by herpes simplex virus type 1 (HSV-1), a widespread virus that affects a large portion of the global population.

According to the World Health Organization (WHO), an estimated 67% of people under 50 worldwide carry HSV-1, although many may never experience visible symptoms. For those who do, cold sores can recur multiple times a year, often triggered by environmental or physiological factors.
What Causes Cold Sores?
Cold sores are caused by HSV-1, which is typically transmitted through oral contact. After the initial infection, the virus remains dormant in nerve cells and can reactivate due to triggers such as:
Stress

Fatigue
Illness or fever
Hormonal fluctuations
Sun exposure
Dental procedures
During reactivation, the virus travels along the nerves to the skin, causing blisters to form, usually near the lips or mouth. In some cases, cold sores may also appear on the chin, cheeks, nostrils, or even inside the mouth.
Cold Sores: Symptoms, Causes, Treatment, and More
Recognizing Cold Sore Symptoms
Cold sores typically progress through the following stages:
Tingling and itching: Many people experience a burning or tingling sensation around the lips a day or two before blisters appear.
Blistering: Small fluid-filled blisters erupt along the edge of the lips or surrounding facial areas.

Oozing and crusting: The blisters may merge and burst, leaving shallow open sores that form a yellowish crust as they begin to heal.
The entire healing process generally lasts 7–10 days, and outbreaks tend to decrease in frequency and severity over time.
Evidence-Based Treatments for Cold Sores
There is currently no cure for HSV-1, but several clinically approved treatments can help reduce symptom duration and improve comfort.
Prescription Antiviral Medications