Cold sores are small, fluid-filled blisters that typically appear on or around the lips. They are caused by the herpes simplex virus (HSV), most commonly HSV-1. These sores can be painful and may cause itching or burning sensations. Cold sores are contagious and can spread through close contact, such as kissing or sharing utensils. Once a person is infected with the virus, it remains in the body and can become dormant. Triggers like stress, illness, or sun exposure can reactivate the virus, leading to new outbreaks. While there is no cure, antiviral medications can help reduce the severity and duration of symptoms.