Blood blisters in the mouth are most often caused by minor physical trauma, like biting your cheek or burning the roof of your mouth with hot food. They appear as dark red or purple fluid-filled sacs, typically on the palate, tongue, inner cheeks, or lips. Most are harmless, heal within a week, and need no treatment. But in some cases, oral blood blisters signal an underlying condition worth investigating.
Physical Trauma: The Most Common Cause
More than half of oral blood blisters trace back to some form of minor injury. The three most frequent triggers are hot foods, dental fillings or crowns, and gum disease treatment. Biting the inside of your cheek is another classic cause. The tissue lining your mouth is thin and packed with tiny blood vessels, so even slight damage can trap blood beneath the surface and form a blister.
Dental injections used for numbing can also cause them. If you’ve ever noticed a blood-filled bump after a filling or cleaning, the anesthetic needle or the procedure itself likely broke a small vessel under the tissue. These blisters are painful but short-lived. They usually rupture on their own within 48 hours and heal completely within about a week without scarring.
Steroid Inhalers and Chemical Irritants
If you use a steroid inhaler for asthma or COPD, the propellant and medication hitting the back of your throat can irritate the mucosa enough to produce blood blisters over time. This is one of the lesser-known triggers, but it’s well documented.
Your toothpaste could also play a role. Sodium lauryl sulfate (SLS), the foaming agent in most toothpastes, is a recognized mucosal irritant. At concentrations above 0.5%, SLS can damage the upper layers of the oral lining, causing inflammation, tissue peeling, and ulceration. Toothpastes typically contain 1 to 3% SLS. Studies comparing SLS-containing toothpaste to SLS-free alternatives found significantly higher rates of mouth sores in people using the SLS versions. If you get frequent oral blisters or ulcers, switching to an SLS-free toothpaste is a simple first step.
Angina Bullosa Haemorrhagica
When blood blisters appear in the mouth without any clear injury, the condition is called angina bullosa haemorrhagica (ABH). Despite its intimidating name, ABH is benign. These blisters develop suddenly in otherwise healthy people, most commonly on the soft palate, tongue, or inner cheeks. They range from about 4 to 30 millimeters across, and there are usually fewer than three or four at a time.
The exact cause of ABH is considered idiopathic, meaning it isn’t fully understood. One theory involves weaker-than-normal connective tissue in the oral lining. Researchers have found that some people with ABH have fewer elastic fibers in their oral mucosa, making the tissue more fragile and blood vessel walls less anchored. This may explain why something as minor as eating crunchy food or even sneezing can trigger a blister. ABH has also been associated with diabetes and high blood pressure, though the relationship isn’t entirely clear.
ABH blisters rupture quickly, often within a day or two, leaving behind a shallow, painless ulcer that heals on its own. No treatment is typically needed beyond keeping the area clean.
Low Platelet Counts
Blood blisters in the mouth can sometimes reflect a more serious problem with your blood’s ability to clot. When your platelet count drops significantly (a condition called thrombocytopenia), blood can leak into the soft tissue of your mouth, forming what clinicians call “wet purpura.” These blisters appear on the inner cheeks, palate, tongue, and lips, and they signal that bleeding risk is elevated throughout the body.
A normal platelet count sits above 150,000 per microliter. Wet purpura tends to appear when counts fall dramatically, sometimes to dangerously low levels. One documented case involved a patient with immune thrombocytopenia (ITP) whose platelets had dropped to just 7,000 per microliter. Causes of low platelets include certain medications, infections, autoimmune diseases, and cancers that affect the bone marrow.
The key difference from a harmless blood blister: wet purpura usually involves multiple blisters, and you’ll often notice other signs of easy bleeding, like frequent nosebleeds, unusual bruising, or tiny red dots (petechiae) on your skin. If oral blood blisters appear alongside any of these symptoms, that combination warrants urgent medical evaluation.
Autoimmune Blistering Diseases
Certain autoimmune conditions cause the body’s immune system to attack the layers of tissue in the mouth, producing blisters that can look identical to ABH. Pemphigus vulgaris is one example. In this disease, the immune system breaks down the bonds between skin cells, creating fragile blisters that form and rupture easily. Mucous membrane pemphigoid is another, targeting the deeper layers of the oral lining.
From the outside, these blisters can be impossible to distinguish from harmless ABH. The difference shows up under a microscope: ABH blisters form beneath the top layer of tissue, while pemphigus blisters form within it, where the cells separate from each other. If blood blisters in your mouth keep coming back, spread to new areas, or don’t heal within a couple of weeks, a biopsy can determine whether an autoimmune condition is responsible.
Vascular Growths That Mimic Blood Blisters
Not every dark, raised bump in the mouth is a blood blister. Hemangiomas, which are clusters of blood vessels that grow and bunch together abnormally, can look similar. They appear as reddish-purple lumps, range from a quarter inch to about two inches wide, and tend to persist rather than rupture and heal. They are benign and not cancerous.
The simplest way to tell the difference: a blood blister appears suddenly and resolves within days. A hemangioma stays put. If you have a dark bump that hasn’t changed or gone away after a couple of weeks, an ultrasound can usually confirm what it is without the need for a biopsy.
What Helps Them Heal
Most oral blood blisters need no intervention. They burst on their own and the tissue underneath heals within a week. Resist the urge to pop them yourself, since breaking the skin barrier increases the chance of infection in a part of the body that’s constantly exposed to bacteria.
While a blister is healing, you can minimize discomfort by avoiding hot, spicy, or sharp-edged foods. Rinsing gently with warm salt water keeps the area clean. If blisters are recurring, look at what might be causing repeated trauma: a rough tooth edge, ill-fitting dentures, a habit of cheek biting, or an SLS-heavy toothpaste. Addressing the trigger is more effective than treating each blister individually.