A cold sore is a cluster of small, fluid-filled blisters that typically appears on or around the border of your lips. The blisters sit on a patch of red, inflamed skin, and they progress through distinct visual stages over the course of 7 to 10 days. If you’re trying to figure out whether a spot near your mouth is a cold sore, understanding what each stage looks like (and what it doesn’t look like) will help you identify it.
The Five Visual Stages
Cold sores don’t appear all at once. They follow a predictable pattern that changes how the sore looks from day to day.
Stage 1: Tingling (no visible sore yet). Before anything shows up on your skin, you’ll feel tingling, burning, or itching in a specific spot, usually along the lip line. The area might look slightly pink or feel tight, but there’s nothing obvious to see. This prodrome phase typically lasts a few hours.
Stage 2: Blistering. One or more small blisters filled with clear fluid appear on the surface of the skin. The skin around and underneath the blisters turns red. The blisters often form in a tight cluster rather than appearing as a single bump, which is one of the easiest ways to recognize a cold sore.
Stage 3: Weeping. Within a few days, the blisters break open. At this point the sore looks red, wet, and shallow, almost like a small raw patch. This is the most contagious stage and often the most painful.
Stage 4: Crusting. As the open sore dries out, a crust forms over it. The scab typically looks yellow or brown. It may crack and bleed if you move your mouth a lot or pick at it.
Stage 5: Healing. The scab gradually flakes away over several days. New skin forms underneath. The whole process from first tingle to fully healed skin usually takes 7 to 10 days without treatment.
Where Cold Sores Show Up
The most common location is right along the border of the lips, where the lip skin meets the surrounding facial skin. They can appear on the upper lip, lower lip, or at the corners of the mouth. Less commonly, cold sores develop on the chin, cheeks, or inside the nostrils. Rarely, they can show up on the nose itself. Wherever they appear, the visual pattern of fluid-filled blisters on inflamed skin stays the same.
How They Look on Different Skin Tones
Most descriptions of cold sores reference red, inflamed skin, but that’s primarily how they look on lighter skin. On darker skin tones, the inflamed patch beneath and around the blisters may appear purple, brown, or simply darker than the surrounding skin rather than red or pink. The fluid-filled blisters themselves look similar across all skin tones, but the base color difference can make cold sores harder to recognize if you’re expecting bright redness. After healing, darker skin tones are also more likely to have a patch of hyperpigmentation (a darker spot) that can linger for weeks after the sore itself is gone.
Cold Sore vs. Pimple
A pimple on the lip forms a single raised red bump, often with a whitehead or blackhead visible at its center. A cold sore starts as a cluster of tiny fluid-filled blisters on a red, swollen base. The key visual differences: pimples have a defined pore at the center, while cold sores have a dome-like, translucent surface filled with clear liquid. Pimples also don’t tingle or burn before they appear, and they don’t go through the weeping and crusting stages that cold sores do.
Cold Sore vs. Canker Sore
Location is the fastest way to tell these apart. Cold sores form on the outside of the mouth, around the lips and on surrounding facial skin. Canker sores form exclusively inside the mouth, on the inner cheeks, inner lips, tongue, or gums. Canker sores are white or yellow with a red border, flat, and oval-shaped. Cold sores are raised, fluid-filled, and clustered. If the sore is inside your mouth, it’s almost certainly a canker sore, not a cold sore.
Cold Sore vs. Impetigo
Impetigo is a bacterial skin infection that can look similar to a cold sore at first glance, especially around the nose and mouth. The difference is in the crust. When impetigo sores rupture and dry, they form a distinctive honey-colored crust that looks thicker and more golden than the yellow-brown scab of a healing cold sore. Impetigo sores also tend to spread more widely across the skin rather than staying in a tight cluster, and they don’t start with the tingling sensation that cold sores do. Impetigo is more common in young children.
Signs a Cold Sore May Be Infected
Cold sores are caused by a virus, but sometimes bacteria get into the open sore during the weeping stage and cause a secondary infection. Signs to watch for include thick yellow or green pus (as opposed to the clear fluid of a normal cold sore), redness and swelling that spreads well beyond the original sore, increasing pain after the sore has already opened, and warmth or tenderness in the surrounding skin. A normal cold sore should start improving after the crusting stage. If it hasn’t begun healing within 10 days, or if swelling is getting worse rather than better, that’s worth medical attention.