The difference between canker sores and cold sores and how to effectively treat both

• Cold sores occur on the outside of the mouth and are caused by the herpes simplex virus.
• Canker sores are blisters inside the mouth that can occur due to injury, nutritional deficiencies, and bacterial infection.
• Both cold sores and canker sores will resolve on their own, but topical ointments can help ease symptoms.

Cold sores and canker sores are relatively common, non-threatening blisters in and around the mouth. Here's how to tell the difference between cold sores and canker sores and how to treat each.

What are cold sores?

Cold sores are blisters that typically appear on the lips or skin around the mouth and nose. They occur as a result of the herpes simplex virus.

According to Brooke Jeffy, MD, a dermatologist at Spectrum Dermatology in Phoenix, Arizona, cold sore symptoms include:

• A burning and tingling sensation
• The appearance of a fluid-filled blister
• Scabbing

"Often, a cold sore outbreak will start with a burning or tingling sensation around the lips. A few days later a fluid-filled blister, or cluster of blisters, will form. These blisters will burst and then scab over as they slowly heal over a one to two-week period," says Jeffy.

What are canker sores?

Canker sores are small sores on the tongue, gums, lips, or inside of the cheeks, says Jeffy. These painful, round sores are often white or yellow with a ring of redness around them.

Symptoms of canker sores include:

• A burning and tingling sensation
• A round white or gray sore with a red border
• Pain inside the mouth

Rare symptoms include:

• Fever
• Sluggishness
• Swollen lymph nodes

How to tell the difference

"Canker sores only occur in the oral tissues inside the mouth, whereas cold sores commonly occur on the outer edges of the lips but also on the skin around the lips or nose," says Jeffy.

Additionally, unlike canker sores, a burning sensation usually precedes cold sores in the area the sore will appear, says Jeffy. If you're unsure which sore you're experiencing, a doctor should be able to make a determination and take a culture or blood test to confirm.

What causes cold sores?

Cold sores are caused by the herpes simplex virus, an incurable condition that exists in two forms: HSV-1 and HSV-2.

Most cold sores are caused by HSV-1, which affects about 67% of people worldwide under the age of 50. However, HSV-2, which is typically associated with genital herpes, can be transmitted to the area around the mouth during oral sex.

People with HSV won't always have active sores, as the virus can remain dormant. However, according to Jeffy and A. Ross Kerr, DDS, MSD, a clinical professor of oral and maxillofacial pathology, radiology and medicine at NYU College of Dentistry, a few factors can activate cold sores:

• Sun exposure
• Increased stress
• Cold temperatures

A cold sore is most contagious when active but can be transmitted at any time through contact like kissing and oral sex.

What causes canker sores?

The exact cause of canker sores is unknown, but according to Jeffy, certain conditions appear to trigger them, such as:

• Injury to the mouth
• Sensitivities to certain ingredients in toothpaste, mouthwash, or foods
• Bacterial infections in the mouth or gastrointestinal tract
• Hormone fluctuations
• Stress
• Certain deficiencies, such as vitamin B-12, zinc, folate, or iron

Canker sores, unlike cold sores, are not contagious.

Diagnosis

Both cold sores and canker sores usually do not require medical attention. However, if you want a diagnosis, a doctor can perform a culture to determine if HSV is present.

Some canker sores may warrant a doctor's visit. "If canker sores are frequent, associated with fever, are extremely painful or very large, they should be evaluated by a medical professional to determine if there are any deficiencies or associated infections or diseases that may be contributing," says Jeffy. "Any sore lasting longer than four weeks should be evaluated by a medical professional."

How to treat cold sores

On average, cold sores take between two and three weeks to heal fully. The following treatments may help reduce discomfort:

• Topical creams and ointments. Kerr says these need to be applied regularly and early on to shorten the length of a cold sore by about a day.
• Oral antivirals such as Acyclovir and Valacyclovir can also reduce the length of active infection, says Kerr.
• Applying a cold compress
• Lip balms and creams
• Reducing stress levels

How to treat canker sores

Canker sores can take up to four weeks to heal fully, but small canker sores will clear within a week or two. According to Kerr, certain steps can improve discomfort and shorten the length of canker sores, including:

• Using topical prescription steroids
• Over-the-counter topical numbing agents
• Mouth rinses that contain the steroid dexamethasone

If a vitamin deficiency or a bacterial infection is triggering your canker sore, you may need to treat this underlying health condition to heal it.

Insider's takeaway

Cold sores are caused by the herpes simplex virus and occur on and around the lips. The exact cause of canker sores is unknown and they occur in the mouth.

While most cold sores and canker sores do not require medical attention, treatments like oral creams and mouthwashes can ease symptoms in both cases.

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