A fever blister on your lip looks like a small cluster of fluid-filled blisters surrounded by red, inflamed skin. The blisters typically form right along the border of your lips, and the fluid inside them is clear or slightly straw-colored. But the appearance changes significantly over the course of about 10 days as the sore moves through distinct stages, so what you see depends on when you catch it.
Where Fever Blisters Show Up
Fever blisters, also called cold sores, form on the outside of the mouth, generally right around the border where the lip meets the surrounding skin. This is the most common spot by far. They can also appear around the nose, on the cheeks, or occasionally inside the mouth, though that’s less typical. If you’re seeing a sore inside the mouth on the soft tissue (like the inner cheek or gums), that’s more likely a canker sore, which is a completely different condition.
What Each Stage Looks Like
A fever blister doesn’t just appear and disappear. It goes through five visual stages over roughly 10 days, and knowing where you are in that progression helps you identify what you’re looking at.
Tingling (No Visible Sore Yet)
Before anything shows up on the skin, you’ll usually feel tingling, burning, or itching in one spot on or near your lip. The skin may look slightly pink or feel tight, but there’s nothing clearly visible yet. This stage is easy to miss if you’re not familiar with it.
Blistering
Within a day or two of the tingling, one or more small blisters appear on the surface of the skin. These are tiny, fluid-filled bumps that often cluster together. The fluid inside is clear or faintly yellow, not white like pus. The skin underneath and around the blisters will be red and inflamed. This is the stage most people picture when they think of a fever blister.
Weeping
After about three to four days, the blisters burst open and drain their fluid. At this point the sore looks like a shallow, red, open wound. It may appear wet or raw. This is the most contagious stage and often the most painful. The surrounding skin stays red and swollen.
Crusting
As the open sore begins to dry out, a crust forms over it. This crust typically looks yellow or brown, sometimes described as honey-colored. The scab can crack and bleed if you move your mouth too much or pick at it, which may restart the crusting process.
Healing
The scab slowly flakes away over the final days. New skin forms underneath, and any remaining redness gradually fades. Most cold sores clear up completely within 10 days without treatment, though some take slightly longer.
How to Tell It Apart From a Pimple
A pimple on the lip area is a single raised bump, usually with a white or yellowish head filled with pus. A fever blister, by contrast, is a cluster of tiny blisters grouped together, filled with clear or straw-colored fluid rather than thick white pus. Pimples also don’t tingle or burn before they appear the way cold sores do, and they don’t go through distinct weeping and crusting stages.
Location is another clue. Pimples can show up anywhere on the face, including on the fleshy part of the lip itself. Fever blisters strongly favor the border of the lip, right where the lip skin transitions to the surrounding facial skin. If you see a cluster of small blisters sitting right on that lip line, especially if you felt tingling beforehand, it’s almost certainly a fever blister.
How to Tell It Apart From a Canker Sore
Canker sores and fever blisters are often confused, but they look quite different and appear in different places. Canker sores are round or oval ulcers with a white or grayish center and a red border. They form inside the mouth, on the tongue, inner cheeks, or gums. Fever blisters form on the outside of the mouth, around the lips. If the sore is outside your mouth and started as a fluid-filled blister, it’s a fever blister. If it’s a flat, open sore inside your mouth, it’s a canker sore.
What Looks Abnormal
A typical fever blister follows the progression described above and resolves within about 10 days. A few signs suggest something else may be going on. If the fluid inside the blisters is thick white or greenish pus rather than clear fluid, the sore may have developed a bacterial infection on top of the viral one. If the sore keeps spreading to new areas of the face, doesn’t begin healing after 10 days, or is accompanied by a high fever, those are reasons to get it evaluated. People with weakened immune systems sometimes experience larger or longer-lasting outbreaks that need medical attention.
First-time outbreaks tend to be more severe than recurrences. If this is your first fever blister, the blisters may be larger, more numerous, and more painful than what you’d see in someone who gets them regularly. Repeat outbreaks are typically smaller and heal faster because your immune system has learned to respond to the virus more quickly.