What Is a Canker Sore?

A canker sore is a small, painful ulcer that forms inside the mouth usually on the inner cheek, lips, tongue, or gums. They're extremely common, not contagious, and typically heal on their own within one to two weeks. Ocotillo Trails Family Dentistry helps patients in San Tan Valley, Gilbert, and Mesa understand what's causing recurring or persistent mouth sores.

San Tan Valley (480) 457-1977
Gilbert (480) 963-9900
Mesa (480) 830-3344

Canker Sores vs. Cold Sores: The Key Difference

These two are often confused, but they’re different conditions with different causes.

If a sore is inside your mouth and you’ve never had a cold sore break out on your lips before, it’s very likely a canker sore rather than a cold sore.

Canker Sore or Cold Sore?

Compare their location, contagiousness, appearance, and cause.

Canker Sores

Location: Inside the mouth—cheek, tongue, gums, or inner lip

Contagious? No

Appearance: Flat, with a white or yellow center and a red border

Cause: Not fully known; often linked to injury, irritation, or stress

Cold Sores

Location: On or around the outside of the lips

Contagious? Yes—caused by a herpes simplex virus

Appearance: Fluid-filled blisters, often in a cluster

Cause: Herpes simplex virus (HSV-1)

Causes of Canker Sores

The exact cause of canker sores isn’t fully understood, but several things are known to trigger them:

Injury or irritation: Biting your cheek, a sharp piece of food, or irritation from braces or a rough dental appliance
Certain foods: Acidic or spicy foods, such as citrus fruits, can trigger sores in people who are sensitive to them
Nutritional deficiencies: Particularly low vitamin B12, iron, or folate
Stress: Emotional or physical stress is a common trigger
Family history: Canker sores tend to run in families
Hormonal changes: Some people notice a pattern tied to hormonal shifts

Symptoms of Canker Sores

A small, round or oval sore with a white or yellow center and a red border
Tingling or burning sensation in the day or two before the sore appears
Pain when eating, drinking, or talking, especially with acidic or spicy foods
Most commonly found on the inner cheeks, inner lips, tongue, gums, or soft palate
One sore at a time in most cases, though several can appear together

A less common form, called a herpetiform canker sore, causes a cluster of many small ulcers at once. Despite the name, it isn’t caused by the herpes virus; it’s still a type of canker sore, just with a different pattern of ulceration.

About Cold Sores

Cold sores, also called fever blisters, are a different condition caused by the herpes simplex virus (HSV-1). Unlike canker sores, they’re contagious and typically appear as a cluster of small blisters on or around the lips rather than inside the mouth.

They often start with tingling or itching before the blisters form, and they tend to crust over as they heal. Because cold sores are viral, they can recur when triggered by stress, illness, or sun exposure, and antiviral treatment—rather than the canker sore remedies below—is usually what helps them heal faster.

If you’re dealing with a sore that matches this description rather than the canker sore pattern above, it’s worth having it evaluated so the right treatment approach is used.

Is It Something More Serious?

Most canker sores are harmless and heal on their own. Certain symptoms or recurring sores are worth discussing with a dentist or doctor.

Have It Checked If

It’s unusually large or especially painful
It hasn’t healed within two to three weeks
You’re getting them frequently or they keep coming back
It’s accompanied by fever, fatigue, or swollen lymph nodes

Why Persistent Cases Matter

Frequent or severe canker sores are occasionally linked to an underlying condition affecting the immune system or digestion, so persistent cases are worth mentioning to a dentist or doctor rather than just waiting them out each time.

Treatment Options

1. Natural Healing

Most canker sores heal without treatment beyond gentle home care, usually within one to two weeks.

2. Topical Gels or Pastes

Over-the-counter topical gels or pastes can coat the sore and reduce pain.

3. Antimicrobial Rinses

Antimicrobial mouth rinses may help prevent secondary irritation.

4. Prescription Medication

A topical corticosteroid or another prescription medication may be recommended for severe or recurrent sores that don’t respond to over-the-counter treatment.

Home Care / What Not to Do

Simple steps can reduce discomfort while a canker sore heals.

Can Help While It Heals

Rinse gently with warm salt water several times a day
Apply a small amount of milk of magnesia directly to the sore with a cotton swab
Use an ice chip or cold compress to numb discomfort
Avoid acidic, spicy, or rough/crunchy foods that can further irritate the sore

Avoid

Rinsing with hydrogen peroxide—it shouldn’t be swallowed and isn’t recommended as a mouth rinse
Picking at or re-irritating the sore, which can slow healing
Assuming it’s “just a canker sore” if it keeps recurring—persistent cases deserve a look

How We Treat Recurring Canker Sores

If canker sores are frequent, unusually painful, or slow to heal, a dental exam can help rule out other causes and determine whether a prescription-strength treatment makes sense. Our General & Preventive Dentistry team can also check whether something in the mouth—like a rough filling or an orthodontic appliance—is contributing to repeat irritation.

Medically Reviewed Information

Medically reviewed by Dr. Matthew Roper, DDS. Last updated September 15, 2026.

Dr. Roper is a licensed general dentist who earned his Doctorate of Dental Medicine from A.T. Still University in Mesa.

This information is for educational purposes and does not replace a professional diagnosis.

Frequently Asked Questions

Are canker sores contagious?

No. Canker sores are not caused by a virus and cannot be spread to another person through contact. This is one of the clearest ways to tell them apart from cold sores, which are contagious.

What causes canker sores?

The exact cause isn’t fully known, but common triggers include mouth injury or irritation, certain foods (especially acidic or spicy ones), nutritional deficiencies, stress, and family history.

How long do canker sores take to heal?

Most heal on their own within one to two weeks. If a sore lasts longer than two to three weeks, it’s worth having a dentist take a look.

What's the difference between a canker sore and a cold sore?

Canker sores form inside the mouth and aren’t contagious; cold sores form on or around the lips, are caused by a virus, and are contagious. See the comparison section above for a full breakdown.

What is a herpetiform canker sore?

It’s a less common type of canker sore that appears as a cluster of many small ulcers instead of one larger sore. Despite the name’s similarity to “herpes,” it isn’t caused by the herpes virus; it’s still a form of canker sore (aphthous ulcer).

Neighborhoods We Serve

Ocotillo Trails Family Dentistry is proud to welcome patients from San Tan Valley and the surrounding communities, including:

Driving Directions to Our San Tan Valley Dental Office

Coming to our office with concerns about canker or cold sores? Ocotillo Trails Family Dentistry is at 40815 N Ironwood Rd #102, San Tan Valley, AZ 85140. Follow N Ironwood Road toward E Ocotillo Road and continue into the property to Suite 102.