A blood blister in your mouth happens when the blood vessels below an existing blister rupture. Some causes include trauma, food allergies, and having a low platelet count.

A blister is a fluid-filled sac that occurs when an upper layer of skin is injured. The fluid, which is generally clear, comes from the injured tissue. When the fluid pools, a blister forms and acts as a barrier, protecting the damaged skin from any additional harm.

In some cases, blood vessels below the injured skin will rupture and blood will fill the blister “bubble,” creating what is known as a blood blister. Like clear blisters, most blood blisters appear where there is friction. For example, you may develop a blood blister on your feet when you wear ill-fitting shoes. Or, you may develop a blister on your hands after gripping a rake or oar for a long period of time. Blood blisters can also appear inside the mouth.

Many oral blood blisters are big enough that you can see them in your mouth or feel them with your tongue. They can occur anywhere in the mouth, but they are often seen on soft surfaces, such as your cheek, tongue, or on the underside of the lips. You may develop only one or several at a time.

Blood blisters in the mouth range in color from dark red to purple, and are typically painful until they pop. Oral blood blisters can make it uncomfortable for you to chew or brush your teeth.

Blood blisters, canker sores, and fever blisters can all appear in the mouth, and they are typically red in color. There are differences, however.

Canker sores

Canker sores usually begin as reddish ulcers instead of the dark red to purple coloring of a blood blister. Canker sores are covered by a white or yellowish film.

Fever blisters

Fever blisters often start with a tingling feeling where the blister will form. Blood blisters, on the other hand, often appear suddenly and without warning. A fever blister may appear along with a fever and swollen lymph nodes. Fever blisters often form on the lips and under the nose instead of inside the mouth.

Several things can lead to the development of an oral blood blister, including:

  • trauma
  • allergies to foods high in acidity
  • low platelet count, which is known as thrombocytopenia
  • angina bullosa hemorrhagica, a rare disorder

Chemotherapy drugs and radiation also can also cause blood blisters in the mouth.


Most oral blood blisters develop following trauma to the mouth, such as biting your cheek, burning your mouth with hot food, or puncturing soft tissue with sharp food, like a chip. In the case of trauma, a blood blister usually develops quickly after the damage takes place.


Certain foods and medicines can irritate the lining of your mouth and lead to the development of blood blisters. You may be more likely to develop blood blisters from allergies to:

  • acidic foods, like citrus fruits
  • cinnamon flavoring
  • astringents, such as those used in mouthwash and toothpaste


Platelets are blood cells that help the blood clot. You can develop a low platelet count for a variety of reasons, including during pregnancy or when taking some medications, such as certain antibiotics and anticonvulsants. It can also occur when the immune system destroys platelets.

Thrombocytopenia can cause blood blisters in the mouth. About 30,000 new cases are diagnosed every year in the United States and 70 percent of them occur in women.

Angina bullosa hemorrhagica

Angina bullosa hemorrhagica is a rare disorder that causes painful blood blisters to suddenly erupt on the soft tissues of the mouth. The blisters last only a few minutes, then spontaneously rupture.

One study estimates that about 0.5 percent of the population have these types of blood blisters. The blisters differ from other blood blisters in that they are not related to any systemic disorder, like thrombocytopenia, and often no cause can be found.

Most blood blisters come and go quickly, and require no medical treatment. Here are some tips for managing them:

  • You can reduce pain with over-the-counter pain relievers and ice packs applied to the injured area.
  • Avoid foods that can irritate the blister, such as hot, salty, or spicy foods.
  • Do not attempt to pop the blister. This increases your risk of infection and delays healing. The blister will pop naturally on its own.

See your doctor if:

  • The blister is so large it’s interfering with swallowing or breathing.
  • It takes more than a week or two to fully heal.
  • It’s so painful it’s interfering with your daily functioning. Your doctor may prescribe a soothing mouthwash that can speed healing.
  • The blisters are recurrent.
  • The blister seems infected. Signs of infection include being warm to the touch, pus draining out of it, and red tissue around the blister.

Blood blisters in the mouth can occur for various reasons. They are generally benign. Most blood blisters are due to trauma and quickly resolve without medical intervention. Being mindful of how and what you eat can help keep them at bay.