Gum sores most commonly result from canker sores (aphthous ulcers), which affect about 20% of the population, or from minor physical trauma like biting your cheek or brushing too hard. But the list of possible causes is longer than most people expect, ranging from viral infections and nutritional gaps to signs of a more serious underlying condition.
Canker Sores
Canker sores are the single most common cause of ulcers in the mouth. They appear as small, round sores with a white or yellowish center and a red border, and they tend to show up on soft, movable tissue: the inner lips, cheeks, underside of the tongue, and the floor of the mouth. A specific subtype called herpetiform aphthous ulcers produces clusters of tiny sores (1 to 3 mm each) that can look alarming but are not caused by a virus.
The exact trigger varies from person to person. Physical trauma is one of the most reliable ones. Vigorous toothbrushing, a sharp bite to the inside of your cheek, or irritation from dental work can all set off an ulcer, especially if you’re prone to them. Stress, hormonal shifts, and certain acidic or spicy foods are other well-known triggers. Most canker sores heal on their own within one to two weeks without scarring.
Herpes Simplex Virus
Herpes simplex virus (HSV) causes a very different kind of gum sore, and distinguishing it from canker sores matters because the treatment and contagiousness are not the same. The first infection, called primary herpetic gingivostomatitis, often happens in childhood. It can bring fever, headache, swollen lymph nodes, and then an eruption of small fluid-filled blisters across the gums. The entire gum line typically becomes swollen, red, and painful.
After that initial infection, the virus stays dormant and can reactivate later as recurrent outbreaks. These tend to appear on keratinized (firm, fixed) tissue like the attached gums and the hard palate, starting as tiny blisters that quickly break open into a cluster of shallow red spots or small ulcers. This location difference is one of the clearest ways to tell herpes-related sores from canker sores. Canker sores favor soft, movable tissue. Herpes sores favor firm, fixed tissue like the gums and roof of the mouth.
Physical and Chemical Irritation
Sometimes the cause is straightforward mechanical damage. Ill-fitting dentures, orthodontic brackets, or a broken tooth edge rubbing against the gum can create a persistent sore that won’t heal until the source of irritation is addressed. These sores are typically in one spot that lines up exactly with whatever is rubbing.
Chemical irritation is less common but worth knowing about. Holding aspirin directly against a sore tooth (a folk remedy some people try) can burn the gum tissue. Whitening products, especially if misapplied or left on too long, can do the same. Chemical burns in the mouth cause deeper tissue damage than you might expect, and the damage can continue even after the substance is removed. If you’ve used a product and notice white, peeling, or raw tissue on your gums afterward, that’s likely the cause.
Oral Thrush
Oral thrush is a fungal overgrowth that can spread to the gums, inner cheeks, tongue, and roof of the mouth. The hallmark appearance is creamy white, slightly raised patches that look a bit like cottage cheese. Underneath those patches, the tissue is red and raw, and scraping or rubbing them can cause slight bleeding.
Thrush is more common in people with weakened immune systems, those taking antibiotics or inhaled corticosteroids, and older adults who wear dentures. It can cause enough soreness and burning to make eating uncomfortable. Unlike canker sores, thrush doesn’t resolve on its own and typically requires antifungal treatment.
Nutritional Deficiencies
If you get gum sores repeatedly without an obvious trigger, a nutritional gap could be playing a role. Three deficiencies have the strongest links to recurrent mouth ulcers:
- Vitamin B12: Essential for cell repair and maintaining healthy mucous membranes. Deficiency leads to increased mucosal sensitivity, redness, and painful ulcers.
- Vitamin C: Critical for collagen production and tissue repair. Low levels cause delayed wound healing, fragile gums that bleed easily, and a higher frequency of small, painful ulcers.
- Folate (vitamin B9): Supports the rapid cell turnover that keeps your oral lining intact. Deficiency disrupts that renewal process, leaving the tissue more vulnerable to erosions and ulcers, often accompanied by a burning sensation.
These deficiencies compromise the mucosal lining’s ability to repair itself and mount a normal immune response. A simple blood test can check all three levels, and supplementation often reduces how frequently sores come back.
Autoimmune and Systemic Conditions
Recurring gum sores can sometimes be an early signal of a condition elsewhere in the body. Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis are among the most notable examples. Mouth ulcers are the most common oral sign of IBD during active flares, and in some cases, the oral sores appear months to a year before any abdominal symptoms develop. In Crohn’s disease specifically, the ulcers tend to be deep with rolled edges, often appearing in the tissue lining the space between the cheeks and gums.
Other systemic conditions linked to oral ulcers include lupus, Behçet’s disease, and celiac disease. If you have frequent mouth sores alongside other unexplained symptoms like joint pain, digestive problems, skin rashes, or fatigue, the sores may be part of a larger picture rather than a standalone issue.
When a Gum Sore Could Be Oral Cancer
Most gum sores are harmless, but a sore that doesn’t heal within two weeks deserves attention. That two-week mark is the standard threshold that prompts further evaluation. Oral cancer can initially look like an ordinary sore, which is exactly why it’s easy to dismiss.
Warning signs that set a potentially serious sore apart from a routine one include: a sore on the lip or gum that bleeds easily and persists beyond two weeks, rough or crusty patches on the gums, unexplained numbness or tenderness in the face or mouth, difficulty chewing or swallowing, unintentional weight loss, or chronic bad breath that doesn’t improve with oral hygiene. Any new, persistent sore or rough spot that lingers past the two-week mark warrants a visit to a dentist or doctor for a closer look.
Relieving Gum Sores at Home
For common sores that you’re confident aren’t serious, several approaches can speed healing and reduce pain. Rinsing with warm saltwater a few times a day is one of the simplest and most effective options. You can also mix equal parts hydrogen peroxide and water and use it as a rinse twice daily.
Over-the-counter numbing gels containing benzocaine provide temporary pain relief, which is especially helpful before meals. Avoiding hot, spicy, and acidic foods while the sore is open prevents further irritation. Staying hydrated and keeping up with gentle oral hygiene helps the healing environment. For sores that are particularly painful or slow to heal, a dentist may prescribe a steroid ointment to reduce inflammation and speed recovery.