A cold sore is a cluster of small, fluid-filled blisters that typically appears on or around the lips. The blisters are often grouped together in a patch, and they change appearance significantly over the course of about 10 days as they progress through distinct stages. If you’re trying to figure out whether a spot on your face is a cold sore, here’s exactly what to look for at each phase.
Where Cold Sores Appear
Cold sores most commonly form along the border of the lips, right where the lip meets the surrounding skin. They can also show up on the skin around the mouth, near the nose, and on the chin. In rare cases, cold sores spread to the eyes, fingers, or other parts of the body.
The location is one of the most reliable ways to identify a cold sore. They form on the outside of the mouth, on the skin surface. If you’re looking at a sore inside your mouth, on the inner cheek or tongue, that’s almost certainly a canker sore, not a cold sore.
The Tingling Stage (Day 1)
Before anything is visible, most people feel a tingling, itching, or burning sensation in one spot on their lip or face. This is the earliest warning sign, and it often starts a day or two before blisters appear. The skin in that area may look slightly pink or feel tight, but there’s nothing dramatic to see yet. If you’ve had cold sores before, this sensation is usually unmistakable.
The Blister Stage (Days 2 to 4)
Within about 48 hours of the first tingling, one or more small blisters appear on the skin. These are the hallmark of a cold sore: tiny, fluid-filled bumps grouped together in a patch. The fluid inside is usually clear or slightly yellowish. The surrounding skin often looks red and swollen, and the area is painful to the touch.
A cold sore rarely looks like a single large blister. Instead, it’s a collection of several small blisters clustered tightly together, almost like a tiny patch of bubbles on the skin. This clustered pattern is one of the clearest visual clues that you’re dealing with a cold sore rather than another type of skin irritation.
The Oozing and Crusting Stage (Days 4 to 7)
After a few days, the blisters burst open. At this point the cold sore looks like a shallow, raw, pinkish-red open sore. It may ooze clear fluid and can feel especially painful during this phase. The small blisters often merge before they pop, creating one larger irregular sore rather than multiple separate ones.
Once the oozing slows, a crust or scab forms over the sore. The scab is typically yellowish-brown and can crack or bleed if the skin around your mouth stretches (eating, yawning, or smiling). This crusting stage often looks the worst cosmetically, but it’s actually a sign that healing is underway.
The Healing Stage (Days 7 to 10)
Cold sores should start to heal within 10 days. The scab gradually shrinks and eventually falls off, revealing new pink skin underneath. This fresh skin may look slightly red or discolored compared to the surrounding area for a few days or weeks after the scab is gone. In the vast majority of cases, cold sores heal without leaving a permanent scar. Scarring is rare and typically only happens when a sore becomes unusually deep or takes much longer than normal to heal.
Cold Sores vs. Canker Sores
These two get confused constantly, but they look quite different once you know what to check. A cold sore is a patch of multiple small fluid-filled blisters on the outside of the mouth, usually along the lip border. A canker sore is a single round sore with a white or yellow center and a red border, and it only forms inside the mouth, on the inner cheeks, lips, or tongue.
Canker sores are not caused by a virus and are not contagious. Cold sores are caused by the herpes simplex virus and are highly contagious, especially during the blister and oozing stages.
Cold Sores vs. Impetigo
Impetigo is a bacterial skin infection that can look similar to a cold sore in its later stages. Both produce blisters that break open and form crusty scabs. The key differences are location and scab color. Cold sores tend to stay on or very near the lips, while impetigo often causes sores around the nose and can spread to the limbs. Impetigo also produces a distinctive honey-colored crust that looks different from the darker yellowish-brown scab of a healing cold sore. Impetigo sores tend to spread more widely across the face, while cold sores usually stay in one tight cluster.
Signs a Cold Sore May Be Infected
A typical cold sore is painful and unsightly, but it heals on its own. Sometimes, though, bacteria get into the open sore and cause a secondary infection. Warning signs include increasing redness that spreads beyond the sore itself, pus (thick, opaque, greenish or whitish fluid rather than the normal clear oozing), worsening pain after the first few days instead of improving, and warmth or swelling that keeps getting worse. If the sore hasn’t started improving after 10 days, or if it spreads toward the eyes, that warrants medical attention. Cold sores that reach the eyes can cause serious complications.