Canker Sores

Written By Sharon Boyd, RDH, BS.       |       Reviewed by Lara T. Coseo, DDS

 1 What are Canker Sores
 2 What Causes Canker Sores
 3 Signs And Symptoms of Canker Sores
 4 Dangers And Health Risks of Canker Sores
 5 How To Prevent Canker Sores
 6 Treatments for Canker Sores
     i.  Conventional Treatment for Canker Sores
     ii. Home Remedies for Canker Sores
 7 Your Questions About Canker Sores Answered
 8 References

What are Canker Sores

What does a canker sore look like?

What are canker sores? Also called aphthous ulcers, canker sores are round or oval sores that occur in the mouth, usually inside the lip, cheeks, floor of the mouth or on the tongue. They may appear white or red, raw and very tender.

Canker sores are different from cold sores as cold sores are due to a virus, and canker sores may be due to irritation, stress or other underlying reasons. Approximately one out of 10 people have recurrent aphthous ulcers, or canker sores.[1]

What Causes Canker Sores

Canker sores can have numerous causes, but are most commonly due to:
  • Trauma or irritation
  • Stress and anxiety (2)
  • Dietary reasons
  • Underlying systemic health issues

They are different than cold sores, as canker sores are not caused due to the herpes virus. There may be serious underlying health problems that can cause you to develop frequent canker sores. See “Dangers and Health Risks” for information about underlying health problems that may cause canker sores. Learn more about periodontal disease causes and 100% pure liquid toothpaste at Trusted Health Products.  

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Signs And Symptoms of Canker Sores


Canker sores are usually smaller than cold sores, only taking up about three to six millimeters of space. They are round or oval with a red or raw appearance. If you have multiple canker sores or canker sores in the throat, it is most likely due to a virus such as the strain that causes cold sores.

Most aphthous ulcers or canker sores are tender and typically last 10 to 14 days. Canker sores on the tongue, canker sores in your mouth, under the tongue, or on the lips are all normal locations. Concerns arise when the canker sores or aphthous ulcers are frequent, recurring or chronic. 

Dangers And Health Risks of Canker Sores

If you have chronic canker sores that recur on a frequent basis, you should know that canker sores or other forms of oral blisters, cold sores or ulcers are a symptom of underlying health problems such as:
  • Gluten intolerance
  • Celiac disease (3)
  • Crohn’s disease
  • Irritable Bowel Disease
  • HIV
  • Nutritional deficiency
  • Leukemia
  • Behcet’s Syndrome
  • Drug induced (Fosamax, beta-blockers, NSAIDS)

If you have a condition such as gluten intolerance, your canker sores may be a natural warning to alert you to alter your diet.

SLS And Canker Sores

Sodium lauryl sulfate – sometimes listed as SLS - is a foaming agent commonly used in commercial dental products, and there is a high probability that it is the cause of canker sores since it is an irritant. This ingredient is commonly found in many products in the home such as body washes, cleansers, shampoos and conditioners, shaving cream, toothpaste, and sunscreen. The intent of SLS is to help provide a foamy and bubbly texture which serves to make you feel clean and refreshed.

You may also find others in the family of sulfates like sodium laureth sulfate (SLES) and ammonium laurel sulfate (ALS). They may pose some dangers to your health. Some people seem to be more sensitive to SLS than others. SLS and the other sulfates can irritate skin. It strips skin from natural oils which leads to dry and irritated skin. The Cosmetic Ingredient Review states that these sulfates should not be used in concentrations of more than one percent, which will prevent it from irritating most people. The Environmental Working Group (EWG) advises consumers to use anything with sulfates with extreme caution.

SLS Studies

Data shows that SLS produces adverse effects on the soft tissues of the oral mucosa, and other recent studies reveal potentially adverse effects on all the tissues of the mouth as well.

Drs. Barkvoll and Brokstad with the University of Oslo in Norway conducted the first notable investigation on the effect of SLS in patients with canker sores (recurrent aphthous ulcers). Their conclusion was that using SLS-free toothpaste, reduced the incidence of canker sores by 60 to 70 percent. This nine-month clinical study "suggested that the denaturing effect of SLS on the oral mucin layer, with exposure of the underlying epithelium, induces an increased incidence of Recurrent Aphthous Ulcers (RAU)." In layman’s terms this means that SLS increases the possibility of painful recurring ulcers on the inside of the mouth.

In another study - Barkvoll and Brokstad state that "Sodium lauryl sulfate (SLS), the most widely used detergent in toothpastes, has been reported to cause adverse effects on oral soft tissues. This double-blind cross-over study indicates that sensitive patients may contract mucosal irritation through SLS in toothpastes. Less toxic detergents...are desirable in oral hygiene products."

SLS in toothpaste is a chemical irritant that has been also associated with sloughing (desquamation) – in layman’s terms the process of shedding dead surface cells from the skin - of the oral tissues (mucosa) and even the reduction of the effectiveness of fluoride to prevent tooth decay. A study conducted by Dr. Herlofson, using toothpaste with different types of detergents, concluded that using toothpaste with SLS significantly increased the incidence of sloughing of the tissues in the mouth (desquamation of the oral mucosa). (European Journal of Oral Science, 104 (Feb 1996): 21-26)

How To Prevent Canker Sores

Preventing canker sores is important for people who have problems with developing aphthous ulcers on a frequent basis. The best way to manage and limit your canker sore outbreaks include:

  • Addressing nutritional deficiencies (iron, vitamin B, folate). Here are some more things to know about oral health nutrition.
  • Using an antimicrobial mouth rinse such as one that contains essential oil to manage germs in the mouth
  • Addressing dietary needs such as avoiding gluten
  • Managing stress and anxiety
  • Improving your immune system through diet, exercise and adequate rest 

Treatments for Canker Sores

Most dental and medical professionals recommend treating canker sores by simply allowing them to heal on their own. If canker sores are frequent and happen more than normal, you will want to get rid of canker sores fast. In severe cases, dentists may prescribe mouthwash for canker sores or lysine for you to have on hand for another outbreak.
Alternative in-office canker sore treatment may also include:
  • Laser therapy (4)
  • Mucosal bandage
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Most remedies for canker sores are those that you can use on your own. To get rid of canker sores and limit discomfort you can:
  • Avoid trigger foods (gluten, citrus).
  • Use an antimicrobial rinse, such as one that contains an essential oil.
  • Apply healing essential oils to the area using a cotton swab. (5)
  • Apply Aloe Vera gel to the wound. (6)
  • Rinse with a solution containing milk of magnesia and liquid antihistamine for topical pain relief. Do not swallow.
  • Dab the ulcer with a cotton swab soaked in one part hydrogen peroxide and one part water.
  • Rinse with salt water solution and cover canker sore with baking soda.

Your Questions About Canker Sores Answered

How do you get canker sores? Canker sores can be caused by various triggers such as irritation or trauma to the area, food allergies, nutritional deficiencies, stress or anxiety.

Are canker sores contagious? Actual canker sores are not contagious. However, cold sores, which are viral in nature, can spread the virus through saliva - such as when sharing food or kissing.

Are canker sores herpes? Canker sores are not herpetic in nature, but cold sores are from a strain of the herpes virus. Before you become alarmed, the herpes virus also causes chickenpox and shingles. It is a different strain than that often associated with the STD.

How long do canker sores last? Most canker sores heal within 10 to 14 days. Sores that last longer than this should be examined by a professional to make sure it’s not something serious.

Why do I keep getting canker sores? Some recurrent sores may be due to underlying systemic conditions like food sensitivities (gluten or acidic foods) or triggered by stress and anxiety.

What’s the difference between cold sores and canker sores? Cold sores are viral in nature, and usually triggered by illness, stress or sunlight. The virus exists in the body and cold sores can only appear in people who have the virus. Canker sores on the other hand are usually from an irritant, stress or dietary reason and are not caused by a virus.

Is it a good idea to put salt on canker sores? No. Putting salt on a canker sore will simply cause the area to become irritated and painful.

How are canker sores formed? Most aphthous ulcers are caused by irritation or trauma, such as hard food poking into the gums, or orthodontic appliances rubbing the inside of your cheeks.

Do they come in groups? Most canker sores pop up one at a time. If you see a cluster of sores in a group, it’s usually a cold sore instead of a typical aphthous ulcer.

Are some canker sores good? Nearly all canker sores cause discomfort. There’s not usually a “good” reason for them being there. However, teething infants or toddlers may have what looks like a small ulcer on their gums when a tooth is coming in.

Do viruses cause them – which ones? Cold sores, also known as “fever blisters,” are a type of oral ulcer that’s caused by a specific strain of herpes. No, not that kind! A different one, just like Chicken Pox.

When do you usually get canker sores? Depending on which type of a sore you have, the ulcer might be caused by illness, hormone changes, orthodontic treatment, trauma (bumping your mouth or an orthodontic wire irritating your cheek) or even an abscessed tooth.

Are canker sores painful? Almost always. Fortunately, a typical canker sore or aphthous ulcer will heal on its own within about two weeks.

Do canker sores get worse? Canker sore pain is usually short lived. If for any reason you have an oral ulcer that lasts for longer than two weeks, you need to seek out dental care to rule out a more serious diagnosis (such as oral cancer or an abscessed tooth.)

Will canker sores swell? Aphthous ulcers usually look flat or sunken in, while cold sores swell and then crust over.

Do canker sores burn? The pain of a canker sore can leave a sharp, tender, or burning sensation in your mouth each time it’s touched or irritated. Symptoms should gradually improve until it’s gone within 10 to 14 days.

Can canker sores cause a fever? The only time a canker sore will cause a fever is if it evolves into a severe lesion and becomes infected, leading to sepsis. Such an occurrence is extremely rare.

Do canker sores cause headaches? No. But if they accompany another illness such as an abscessed tooth, there’s a risk of referred pain that may mask itself as a headache.

Can canker sores cause swollen lymph nodes or glands? Unless the ulcer is caused by the cold sore virus (fever blisters) then it’s unlikely that you’ll have any swollen lymph nodes.

Can canker sores cause ear pain? Not usually. However, ulcers on your tonsils may mimic pain in other areas because of their close proximity to your ears.

Can canker sores be sore on your gums too? Yes. Ulcers typically cause significant pain wherever they are. Aphthous ulcers can appear on your gums, tongue, lips, cheeks, palate, or in the roof of your mouth.

Are canker sores a virus or are they caused by a virus? Regular canker sores aren’t caused by viruses. But the ulcers associated with “cold sores” and “fever blisters” are caused by a specific strain of herpes simplex. As such, the virus can hide inside of your body and pop up at times when your immune system is weak.

Are canker sores an autoimmune disease? Certain types of medical and autoimmune conditions can increase your rate of getting oral ulcers. For instance, Behcet’s disease and gastrointestinal reflux disease are both linked with canker sores. So, if you get ulcers on a frequent basis, you might need a medical screening.

Can canker sores be caused by stress? Yes. Some people do find that stress (including illnesses, menses, and extra time in the sun) can raise the risk of getting canker sores.

Can canker sores get infected? Yes, but it’s not likely. If you practice good oral hygiene and clean your mouth daily, the risk of getting an infected canker sore is fairly low. Rinse your mouth thoroughly several times per day with a non-alcoholic mouthwash to keep the area around your canker sore as clean as possible.

Are canker sores genetic? Some people seem to be more prone to ulcers, giving the idea that canker sores are a genetic trait. However, ulcers such as cold sores are viral in nature and not genetic.

Are canker sores dangerous? It’s not unheard of for some types of ulcers – such as cold sores – to spread closer to areas like your eyes. In such instances it can be extremely dangerous and requires immediate medical intervention.

Are canker sores contagious? While canker sores are not contagious, cold sores are. Since the latter is caused by a virus, kissing anyone or sharing food with someone who has an active cold sore can allow the virus to pass from person to person.

Are they contagious to babies? If it is a cold sore ulcer/fever blister, yes. Just to be safe, never kiss a baby or allow the baby to touch your mouth if you have any type of ulcer or canker sore. In fact, it’s best not to touch other people’s babies on their hands or face, because of the risk of exposing them to germs.

Are canker sores cancer? Oral cancer can look like a canker sore. If you have any type of oral ulcer that doesn’t heal within 10 to 14 days, you need to get screened by a dentist.

Are canker sores a form of HIV or herpes? Having HIV/AIDS can raise your risk of getting ulcers on a frequent basis. Additionally, the herpes strain (which also causes Chicken Pox and Shingles) is also responsible for cold sores which are a type of oral ulcer.

Are canker sores a sign of strep throat? Not usually. However, one of the signs of strep throat is white patches on the back of the throat and tonsils, which may look like ulcers.

Are canker sores caused by stress? Any time your immune system is suppressed, you can be more prone to illness or getting ulcers and cold sores. Stress is a common contributor.

Can canker sores cause tooth pain? If your ulcer is actually a fistula – which is a sore that’s draining because of an abscessed tooth – then you might also experience toothaches and moderate to severe tooth pain.

Can canker sores cause jaw pain? No. Ulcers don’t usually have anything to do with TMJ pain. But if the sore is further back in your mouth or you’re clenching your teeth because of stress, jaw pain might coexist with your canker sore.

Are canker sores normal or common? Yes. Most people get ulcers every now and then. It’s only a problem if you get canker sores on a frequent basis (such as every few months).

Are canker sores common in pregnancy? No, but some women do find that hormonal changes do trigger their chances of getting canker sores and fever blisters.

Can canker sores be painless? Not usually. Canker sores tend to be pretty irritating, but the level of pain that they cause may depend on which part of your mouth that they’re in. Some areas may get irritated more than others because of how often it’s touched.

Are canker sores from germs? Sometimes infections like abscessed teeth (which are caused by germ infections in your gums or tooth roots) can cause sores on your gums. But canker sores aren’t usually germ in nature.

Can you pop a canker sore? No. If you have visible blisters from a cold sore, popping it can actually make the sore worse or spread to other areas. It’s also possible for fever blisters to spread to your fingers.

Are canker sores hard or soft? Soft. But your tongue will usually feel some sort of a texture difference as it rubs over the area. If you have a fever blister, the top of the sore will crust over after several days and feel harder than the areas around it.

What do canker sores look like? Small canker sores are usually less than two to three millimeters wide. They’re circular or oval, with a white or red surface and red border. Large aphthous ulcers can get wider than a centimeter and be extremely painful. But if you have a cold sore/fever blister, it will start out as tiny blisters or bubbles and then evolve into a larger sore that crusts over.

Will canker sores keep getting bigger? Once you notice a canker sore, it’s usually about as large as it’s going to get. If they get larger and don’t improve after a few days (or you’re in too much pain to eat) then you should see a dentist.

Do canker sores look red? Since your mouth is highly vascular, tiny sores can easily take on a red appearance. Especially if the outer layer of your skin is irritated.

Can canker sores turn white? Yes. Once the ulcer starts to heal over, the new layer of mucosa (skin) will usually look white.

Can canker sores cause bad breath? Necrotic (dying) tissues are known for contributing to halitosis. Keeping your mouth clean when you have ulcers can reduce your chances of getting bad breath. But since brushing and flossing may be too painful, consider adding an antimicrobial, alcohol-free mouthwash into your oral hygiene routine.

Can canker sores cause a sore throat? If you get ulcers close to the back of your mouth or on your tonsils, it can make your throat too sore to comfortably swallow or eat.

Can canker sores make you sick? If you have a secondary illness, it’s usually a suppressed immune system that raises your risk of getting ulcers, not the other way around. But if you have a severe canker sore or cold sore that gets infected, it could possibly make you ill.

Do you get canker sores when you are sick? Traditional canker sores pop up when your skin is irritated or from flare-ups because of hormones, intestinal issues, or autoimmune diseases. They won’t always form when you’re sick, but you’re more prone to getting them if you’re ill.

Do canker sores bleed? Not usually. But if you accidentally irritate a canker sore when you’re eating and brushing your teeth, it may bleed more easily than the skin around it.

Do canker sores have pus? Ulcers that release pus are usually not canker sores. It’s more likely that you have a cold sore 'fever blister' or a draining dental abscess.

Can canker sores spread? If it is a viral cold sore, then yes. It can spread across your mouth, onto your hands, into your eyes, or to other people.

Will canker sores come back? Canker sores tend to go away within two weeks and not come back, unless there’s a secondary cause that’s irritating the area. But cold sores do come back from time to time, depending on your immune system.

Do canker sores itch? Canker sores tend to burn and sting, but cold sores cause more of a tingling and itching sensation when they first start to pop up.

Do canker sores sting? If you bump an ulcer, it will usually cause a sharp or stinging sensation for a minute or two.

Can they appear on your lips? Canker sores tend to only form inside of your mouth, but fever blisters can form on your lips and outside of your mouth.

Can canker sores cause lip swelling? If the ulcer is severe enough, then yes. Aggressive canker sores and cold sores can cause visible swelling on your lip.

Why are there canker sores on my tongue? Your entire mouth is covered in mucosa, which is the soft tissues that are highly vascular. Your tongue is no different, which is why you can get ulcers on it too!

Will canker sores go away? Rest assured that most canker sores will heal on their own within 10 to 14 days. If they do not, then it’s likely not an ulcer after all.

Do canker sores scab? Cold sores crust over about halfway through their cycle, but canker sores do not.

Will canker sores grow? Most ulcers stay about the same size until they go away, but fever blisters tend to get larger for a few days after they first start developing.

Will canker sores heal on their own? Unless the ulcer is actually an abscessed tooth, you can expect your canker sore to resolve on its own within two weeks (as long as the source of trauma – such as an orthodontic appliance – isn’t irritating the area any more.)

What do canker sores look like when they are healing? Canker sores tend to look the same from day one to just before they heal. Gradually, the skin over the top of them will start to re-grow and the area will begin to blend in with the mucosa around it.

Do canker sores need to be kept dry? No. A dry mouth might actually cause the canker sore to irritate you even more.

Are there any foods that cause canker sores? Acidic and salty foods including things like tomatoes, lemons, etcetera make some people get oral ulcers more frequently.

What should I eat now that I have canker sores? Since canker sores can be so painful, eating might be a challenge. Stick to soft or cool foods, like cottage cheese, pudding, and gelatin if you’re not able to keep a normal diet by chewing on the other side of your mouth.

Are there any home remedies for treating canker sores? There are dozens of home remedies for canker sores, but there’s nothing scientifically proven to speed up the healing process. If you’re prone to getting cold sores, your dentist can prescribe a medication to keep on hand which might shorten the length of your fever blister. To prevent ulcers from getting worse, be sure to keep your mouth clean by brushing, flossing, and using an alcohol-free antimicrobial rinse. 

Is salt good for canker sores? No. Just like the old saying, “Pouring salt on an open wound,” adding salt to a canker sore can be extremely painful.

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    7. Herlofson BB, Barkvoll P., Department of Oral Surgery and Oral Medicine, Dental Faculty, University of Oslo, Norway. "Sodium Lauryl Sulfate And Recurrent Aphthous Ulcers. A Preliminary Study."

    8. Herlofson BB, Barkvoll P., Department of Oral Surgery and Oral Medicine, Dental School, University of Oslo, Norway. "Oral Mucosal Desquamation Caused By Two Toothpaste Detergents In An Experimental Model," Eur J Oral Sci 1996 Feb;104(1):21-6

    9. European Journal of Oral Science, 104 (Feb 1996): 21-26) The influence of triclosan, zinc or propylene glycol on oral mucosa exposed to sodium lauryl sulphate /

Article Written By Sharon Boyd

Sharon has been a Registered Dental Hygienist since 2001. She also holds a Bachelor of Science degree in Human Relations and Business. In 2011, she began implementing her dental knowledge into freelance writing services that aided dentists, product designers, continuing education providers and web marketing firms for their online and distribution purposes. She has since bridged her services into the medical and cosmetic surgery fields.


 Lara T. Coseo, DDSArticle Reviewed by Dr. Lara Coseo

Lara T. Coseo, DDS, is a 2004 graduate of Baylor College of Dentistry.  She has 13 years of experience practicing general dentistry.  She currently serves as a part-time faculty instructor at Texas A&M College of Dentistry and writes dental website content and blog material.



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