Canker sore or cold sore: What’s that red thing on your lip?

Woman hiding a cold sore on her lip

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Is it a cold sore, herpes simplex, canker sore, acne, or something else? There are several things that can be causing a painful red spot on your lip.

Here, a physician offers some information about the differences.

What the doctor says

The question: “I have had an odd red bump on my top lip, on the border between my lip and my normal skin. I’ve never had this before, and I’m not sure if it’s a cold sore or herpes. How do I know?”

Mouth sores are commonly confused, so let me explain some common types.
What are canker sores?

These are small, often clear or white-looking ulcers that appear in the mouth and last for about a week. They are painful. They typically occur in people between 10-30 years of age, and often occur at the site of a previous cold sore or at a place where you bit the inside of your cheek, lips or gums.

Canker sores also can be on the tongue or on the roof of your mouth. They are usually flat and don’t contain fluid. They are not contagious and are not caused by a virus or bacteria.

You may notice a tingling or burning sensation in the area prior to the appearance of the sore. They can be triggered or made worse by stress or by certain acidic fruits and vegetables such as lemons, oranges, pineapples, apples and tomatoes.

In people with braces, dental work or dentures, these devices can rub on the gums, causing trauma to the area, and then a canker sore can develop.

In most people, canker sores occur only three to four times per year. If you notice sores occurring more often than that, see your health care provider.

This could indicate that you have a nutritional problem, such as low vitamin B-12, zinc, iron or folic acid. It also may mean you have an ulcerating gastrointestinal disease like Celiac disease (a disorder where you can’t tolerate gluten) or Crohn’s disease (a disorder that can be throughout your intestinal tract).

Cold sores

In your question, you ask if you have a cold sore or herpes. Cold sores are actually caused by the herpes simplex virus (HSV), so you are in essence talking about the same thing when you say “cold sores” and “herpes.”

These should be distinguished from canker sores, which are different and not caused by a virus.

In cold sores or fever blisters, the herpes virus replicates and damages the skin, causing small, painful groups of fluid-filled blisters.

Unlike canker sores, cold sores are contagious and can be given to other people through contact.

Cold sores are usually found outside of the mouth — around the lips, under the nose or on the chin. They often have a red border or base, and there are one or more fluid-filled bumps in the center that look clear or yellow.

The cold sores last about one to two weeks, but once the skin heals, the herpes virus still lies dormant in the nerve cells, so you are never actually “cured.”

Over half of the US population is infected with the herpes virus that causes cold sores, but only a few people ever develop cold sores.

Triggers for cold sores include stress, menstruation and fever. To treat cold sores, see your physician at the first signs of an outbreak. We can provide anti-viral creams or pills to help shorten the duration of symptoms.


Sometimes it is difficult to distinguish between a cold sore and a pimple. Some pimples have a red base and a fluid-filled dot in the middle, with pus inside. Pimples, however, are usually not as painful as cold sores. Also, they usually have only one fluid-filled area in the middle, and often will be accompanied by other pimples elsewhere on the face that look similar.

If you are a pimple “popper,” try to avoid doing so. First, it spreads bacteria. Second, if your sore is actually a cold sore, you will only aggravate the area and make it worse.

There are other conditions that can cause mouth sores, ranging from ulcers to cancer. So if your sore doesn’t fit the descriptions above or lasts for longer than two weeks, you should see your doctor.

Jacqueline Gerhart, MD

Jacqueline Gerhart, MD

Dr. Gerhart is a Wisconsin native and completed undergraduate degrees in Biomedical Engineering and Neuroscience at UW-Madison. Her special interests include women's health, sports medicine, mental health and minor surgical procedures. Dr. Gerhart is currently practicing full-spectrum family medicine, including maternity and inpatient care. Note: This is general health information and is not specific advice intended for any particular individual(s). It is not a professional medical opinion or a diagnosis. Always consult your personal healthcare provider about your concerns.

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