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Complex Canker Sores: What They Are and How To Treat Them

A woman uses the Luminance RED device on the complex canker sore in her mouth.


If you’re part of the nearly 25% of the global population that suffers from canker sores, you understand that a simple mouth sore can disrupt your entire life. So when you’re dealing with a complex canker sore, you might feel especially hopeless.

If you’re frequently bothered by canker sores that make your life miserable and never seem to disappear, you may have recurring complex canker sores. Read below to learn how to identify and treat these painful mouth ulcers.

Complex vs. Simple Canker Sores

First, let’s take a close look at complex vs. simple canker sores. These two types of canker sores have a few key differences. 

A canker sore (also called an aphthous ulcer) is a shallow white- or yellow-colored lesion with an inflamed pink or red border. This mouth sore can form anywhere on the soft tissue inside your mouth, including the roof of your mouth, the insides of your cheeks, your gums, and on or under your tongue

Different types of canker sores can be distinguished by their size. Simple canker sores usually measure between one and four millimeters, while the more aggressive complex canker sores may measure five millimeters or larger. 

When looking at complex vs. simple canker sores, remember that complex sores aren’t just bigger they’re also deeper, more painful, and take more time to heal. Most cankers heal on their own within a week or two, but a complex canker sore can take six weeks or longer to heal completely.

Other symptoms that can accompany a complex canker sore include:

  • Fever
  • Swollen lymph nodes
  • Lethargy

If you’re experiencing any of these symptoms alongside a complex canker, chances are your mouth lesion is a side effect of a more serious underlying medical issue.

Complex Canker Sore or Cold Sore?

Some people confuse complex cankers with cold sores, but the underlying causes of these two conditions are very different.

Cold sores, also referred to as oral herpes or fever blisters, are caused by a virus called the herpes simplex virus (HSV). HSV is very contagious, and the virus spreads easily to others through oral contact, such as kissing or sharing eating utensils. HSV can also spread to the genitals through oral-to-genital contact, leading to genital herpes.

By contrast, aphthous ulcers are not contagious at all, and they aren’t caused by a virus.

A cold sore is a blister that typically forms on the outside of the mouth or around the lips. The fever blister fills with fluid, bursts, and crusts over. The scab eventually falls off, revealing completely healed skin beneath.

Cankers, on the other hand, only form on the soft tissue inside the mouth, and they don’t fill with fluid or scab over.

What About Herpetiform Canker Sores?

Don’t confuse complex canker sores with herpetiform canker sores, another type of mouth lesion frequently mistaken for the herpes virus. 

This uncommon type of canker sore presents as a cluster of tiny lesions inside the mouth. These lesions often occur so close together that they appear to merge into one large sore that closely resembles a complex canker sore.

Again, herpetiform cankers only occur inside the mouth, unlike herpes blisters, which occur outside the mouth.

Infographic: Complex Canker Sores: What They Are and How to Treat Them

What Causes Complex Canker Sores?

Complex canker sores often develop as a complication of an underlying health issue or disease, which only a medical professional can diagnose.

In other cases, the cause may be something simple, such as an allergic reaction to a new food. Keep reading to learn some of the most common causes of complex canker sores.

Autoimmune Diseases

Your immune system normally works with your body to protect against foreign invaders — but for people with autoimmune diseases, that’s not always the case. 

Celiac disease, for example, is a severe autoimmune disease in which the body attacks the small intestine at the introduction of gluten. The damage these attacks cause interferes with the body’s ability to absorb essential nutrients. Over time, untreated celiac disease creates serious health complications, including oral health issues such as complex canker sores, enamel defects, and tooth decay.

Other autoimmune diseases linked to complex canker sores include inflammatory bowel disease, lupus, and Behçet’s disease. 

Hand-Foot-Mouth Disease

Mouth ulcers, including complex canker sores, are a common symptom of hand-foot-mouth disease. These ulcers are most likely to occur on the inside of the cheeks or on the tongue.

While adults are occasionally diagnosed with hand-foot-mouth disease, it’s much more likely to affect children, particularly babies and children under five years old. 

Mineral or Vitamin Deficiencies

Mineral and vitamin deficiencies can cause serious health issues. Substances like iron, zinc, folic acid, vitamin C, and vitamins B1, B2, B6, and B12 are fundamental to your core health and wellness. When untreated, deficiencies in these vitamins can contribute canker sore development.

Zinc, for example, is an essential trace element the body needs in small doses each day to properly function. It supports hormone production, immunity, and digestion. Fortunately, zinc is readily available in most multivitamins and mineral supplements, just like many of the minerals and vitamins your body needs to maintain optimal health.

In addition to taking supplements, you can avoid vitamin deficiencies by eating a well-balanced diet. For example, zinc is present in grains, legumes, and many high-protein foods.

With proper levels of the substances your body needs, you can avoid the mineral and vitamin deficiencies that lead to mouth ulcers. 

Oral Care Allergies

A severe allergic reaction to specific oral care products may also trigger severe canker sores.

Toothpaste and mouthwash products containing sodium lauryl sulfate (SLS) are especially notorious for irritating the mouth. SLS is a “surfactant” that creates cleansing and foaming action. Though the United States Food and Drug Administration (FDA) claims SLS is safe, thousands of studies associate SLS with skin irritation and organ system toxicity.

Try removing certain oral care products from your diet or daily routine for a few weeks. If your severe canker sore outbreaks stop, that indicates the product is the cause.

When experimenting with eliminating irritating oral care products, however, be sure to use quality alternatives that help you maintain good oral health. Besides leading to tooth decay, poor oral hygiene can also contribute to the formation of oral ulcers.


Certain types of foods may trigger mouth lesions to form, even if you’re not allergic to them. A few common examples are:

Use caution when consuming any food that’s abrasive or has hard edges. These foods can cut the inside of your mouth, leading to more lesions.

Infographic: Complex Canker Sores: What They Are and How to Treat Them

Treatment Options for Complex Canker Sores

A variety of natural remedies and over-the-counter oral and topical products can treat complex canker sores and other mouth ulcers.

Keep in mind that because complex canker sores are larger and more aggressive than regular canker sores, the products used to treat regular cankers may not work with the same efficacy on complex cankers.

Mouth Rinses

Antimicrobial rinses reduce the number of bacteria and microbes in the mouth, which can protect the gum tissue from future canker sore outbreaks. The deep cleaning effect of antimicrobial rinses can also control plaque and prevent mouth sores from becoming aggravated by excess bacteria. 

Rinses such as Listerine, Peridex and PerioGard are all popular options for people who experience frequent canker sore outbreaks. 

Oral Medications

Though there are no available pharmaceutical medications that treat canker sores, you can alleviate your pain and discomfort using over-the-counter oral medications like ibuprofen, acetaminophen, or naproxen. Zinc throat lozenges may also help reduce canker sore symptoms for a short time. 

Topical Analgesics

Over-the-counter topical products can provide temporary numbing for painful sores. Anesthetics like benzocaine (Kank-A® and Orajel®) are safe and effective for any type of mouth lesion, though you should not use them over a large area. Apply these local anesthetics several times a day to relieve discomfort in adults and children over the age of two.  

Home Remedies

A popular remedy for canker sore pain is blending milk of magnesia, best known by the brand name Maalox®, with Benadryl® or another antihistamine to dab on the lesion. Milk of magnesia is an antacid that coats your canker sore to prevent irritation, while the antihistamine treats inflammation and creates a sedative effect.

There are several other home remedies for mouth sores you may already have in your cabinets at home:

Before using a home remedy, make sure you know how to do so safely. For example, dilute products like hydrogen peroxide and apple cider vinegar with water before applying them to your cankers.

Light Therapy

Red light therapy is a great natural treatment option for canker sores, without any risk of side effects or toxicity. Powerful, medically optimized red light can shorten the healing time and decrease the frequency of canker sore outbreaks, including complex canker sores.

The Luminance RED is a handheld light therapy device that’s specifically designed for canker sores and other mouth ulcers.

When to See a Doctor for Complex Canker Sores

If you’re suffering from complex vs. simple canker sores, you likely need to see a medical professional.

Make an appointment with your regular doctor as soon as possible if you experience any of the following symptoms:

  • Fever
  • Swelling of your lips or face
  • Toothache near the canker sore
  • Tender gums
  • Enlarged lymph nodes in the neck

If your complex canker sores are accompanied by any other serious medical symptoms, such as extreme lethargy, weakness, dizziness, or trouble breathing, seek emergency medical treatment right away.

Frequent complex canker sores that take an exceptionally long time to heal can be a sign of an underlying medical condition. If your mouth sores are recurring or affect your normal functioning, consult your doctor for a diagnosis.

How to Prevent Complex Canker Sores From Recurring

The only thing better than a fast-healing canker sore is a canker sore that never develops at all!

In addition to seeing a doctor, follow these tips to help avoid future complex canker sore outbreaks:

  • Avoid acidic foods like citrus fruits, tomatoes, and coffee
  • Improve your sleep habits
  • Try new stress management techniques
  • Take daily vitamins
  • Improve your dental hygiene

By combining your doctor’s expert advice with small yet powerful lifestyle improvements, you’re much better equipped to manage and prevent complex canker sores in the future!



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