Gum ulcers are most commonly caused by physical trauma, viral infections, or canker sores triggered by stress and immune responses. Less often, they signal a nutritional deficiency, a medication side effect, or a systemic disease. The cause usually determines where the ulcer appears, how long it lasts, and whether it comes back.
Canker Sores vs. Herpes: Two Different Problems
The two most common types of mouth ulcers, canker sores and herpes sores, behave differently on gum tissue. Canker sores (aphthous ulcers) typically show up on soft, non-keratinized surfaces like the inside of the cheeks, the floor of the mouth, and the sides of the tongue. They can appear on the gums, but it’s less typical. Herpes simplex virus, on the other hand, targets the gums directly. A primary herpes outbreak almost always involves the gingiva and can affect the hard palate and the top surface of the tongue.
This distinction matters because the two require different responses. A herpes outbreak, especially the first one, often comes with a high fever (sometimes reaching 104°F), swollen gums, blisters that pop and leave ulcers, difficulty swallowing, and significant mouth pain. It’s caused by herpes simplex virus type 1 and is most severe the first time, usually in young children. Canker sores, by contrast, don’t come with fever or blisters. They start as raised round spots that quickly become shallow, painful ulcers.
Physical Trauma and Irritation
The gums are especially vulnerable to mechanical injury, and that injury is one of the most straightforward causes of ulceration. Orthodontic brackets, wires, and retainers create constant friction against the gum tissue, disrupting the protective mucosal layer and causing localized inflammation that turns into an ulcer. Poorly fitted appliances, over-tightened wires, and rough or sharp edges make the problem worse. Even the material matters: traditional nickel brackets can trigger a hypersensitivity reaction in some people, leading to swelling and ulceration beyond simple friction damage.
Outside of orthodontics, vigorous toothbrushing with a hard-bristled brush can abrade the gumline. Biting the inside of your mouth, eating sharp or crunchy foods, and burns from hot drinks or food all qualify as oral trauma. Teeth grinding (bruxism) can also worsen mechanical irritation, particularly if you already have dental hardware.
Stress, Immune Response, and Genetics
Canker sores remain somewhat mysterious. The damage is driven primarily by T-cells, a type of immune cell, along with inflammatory signaling molecules like TNF-alpha. In practical terms, your immune system attacks a small area of oral tissue, and researchers still aren’t entirely sure why. What is clear is that canker sores run in families, and stress is a reliable trigger for people who are prone to them.
Certain foods, including chocolate, peanuts, and eggs, can make symptoms worse in some people, though no study has proven food allergies directly cause canker sores. Minor canker sores account for about 85% of cases and typically heal within one to three weeks. They recur, sometimes frequently, sometimes after long gaps.
Nutritional Deficiencies
Low levels of iron, vitamin B12, and folate are consistently found in people with recurrent mouth ulcers. In one study of 273 patients with recurring canker sores, about 20% had anemia, 20% had low iron, roughly 5% were deficient in B12, and about 3% were low in folate. These numbers suggest that while nutritional gaps aren’t the most common cause, they’re common enough to be worth checking, particularly if your ulcers keep coming back without an obvious trigger. Correcting the deficiency often helps reduce how frequently ulcers appear.
Medications and Chemical Irritants
Several common medications can cause or contribute to oral ulceration. NSAIDs like aspirin and naproxen are known culprits. One specific and avoidable cause: placing a crushed aspirin directly against gum tissue to treat a toothache. This creates a chemical burn that shows up as a white-to-yellow wrinkled lesion with sloughing tissue. Some blood pressure medications, including certain ACE inhibitors and angiotensin-receptor blockers, can also cause chemical burns or swelling of oral tissue.
Antiseptic mouth rinses containing chlorhexidine can occasionally trigger an allergic contact reaction in the mouth. Inhaled corticosteroids used for asthma or allergies, if not rinsed out after use, can irritate oral tissues as well. Sodium lauryl sulfate (SLS), a foaming agent in many toothpastes, is another well-known irritant that some people find triggers canker sores. Switching to an SLS-free toothpaste is a simple first step if you suspect this connection.
Hormonal Changes
Hormonal shifts, particularly progesterone spikes, are linked to gum ulcers in some women. Progesterone peaks in the days just before your period, and this surge can trigger canker sores along with other oral changes like gum sensitivity and swelling. If you notice a pattern of ulcers appearing in the day or two before menstruation, hormones are likely playing a role. Pregnancy and menopause, both periods of significant hormonal fluctuation, can also increase susceptibility.
Systemic Diseases
Recurring mouth ulcers are sometimes an early sign of a broader condition. Behçet’s disease, a rare inflammatory disorder, produces painful mouth sores that look identical to canker sores. They start as raised round lesions, quickly ulcerate, heal in one to three weeks, and then come back. The difference is that Behçet’s also causes genital ulcers, eye inflammation, and skin lesions. Crohn’s disease and other inflammatory bowel conditions can also produce oral ulceration as part of widespread inflammation.
Large ulcers that are unusually slow to heal should raise concern about HIV, which can cause protracted aphthous ulcers lasting weeks or even months. Ulcers appearing alongside joint pain, eye problems, fever, or swollen lymph nodes point toward a systemic cause that warrants thorough evaluation.
How Long Healing Takes
Most minor canker sores heal on their own within one to three weeks. With treatment, about 21% of patients see complete healing within three days, compared to 8% of untreated patients. Topical steroid pastes (applied directly to the ulcer) can reduce pain and shorten how long each episode lasts, though they don’t prevent future outbreaks. Antiseptic rinses can reduce the severity and pain of an ulcer but similarly don’t change how often they recur. Over-the-counter oral adhesive pastes that form a protective film over the ulcer can also help with pain and speed healing slightly.
The critical timeline to remember is two weeks. A gum ulcer that persists beyond two weeks without improvement, or one that keeps growing, needs professional evaluation. A non-healing ulcer can be a sign of oral cancer, which may present as a persistent sore, a white or reddish patch, a lump, loose teeth, or ear pain. This doesn’t mean every lingering ulcer is cancer, but it does mean the two-week mark is when watchful waiting should end.