One of the most useful things to understand about cold sores is that visible blisters are not always the first sign of an outbreak.
Many people experience a preliminary stage known as the prodrome. During this stage, the affected area may tingle, itch, burn, or feel unusually sensitive. These sensations can begin hours before a blister becomes visible.
Recognizing this early stage matters because antiviral treatment generally works best when started promptly, ideally at the first warning signs.
After the initial tingling, small fluid-filled blisters may appear in a cluster. The surrounding skin can become red, swollen, and tender. The blisters may then rupture, leaving shallow sores that gradually crust over and heal.
Some people experience discomfort when eating, drinking, smiling, or moving their lips. Others develop only mild symptoms and may barely notice the outbreak.
A first episode of oral herpes can sometimes be more extensive than later recurrences. Symptoms may include fever, swollen lymph nodes, sore gums, and painful lesions inside the mouth. However, many initial infections cause few or no obvious symptoms.
Not every sore around the mouth is herpes. Impetigo, contact dermatitis, irritation, and other conditions can produce redness, crusting, or blisters. If the appearance is unusual or the diagnosis is uncertain, a healthcare professional may examine the lesion and, when appropriate, take a swab for testing.
People who repeatedly develop cold sores often learn to recognize their own early symptoms. Keeping a prescribed antiviral medication available, when recommended by a clinician, can make it easier to begin treatment quickly.
Avoid picking or squeezing the blisters. Doing so can irritate the skin, delay healing, and potentially introduce a secondary bacterial infection.
If a lesion does not heal within about two weeks, is unusually severe, or keeps recurring frequently, seek medical advice. Prompt evaluation is particularly important for people with weakened immune systems or sores close to the eyes.