Oral Trauma: This is the most likely cause of blood blisters in the mouth, resulting from accidental bites, dental procedures, or other forms of mouth injury. The trauma causes blood vessels to rupture, leading to the formation of blood blisters.

Oral Lichen Planus: An inflammatory condition that can cause lesions and blisters in the mouth, including blood blisters, due to immune system reactions.
Aphthous Ulcers: Also known as canker sores, these can sometimes appear as blood blisters, especially if they become irritated or infected.
Mouth Ulcers: Various types of mouth ulcers, such as those caused by herpes simplex virus, can initially appear as blood blisters before they rupture.

Oral Cancer: Although less common, blood blisters in the mouth can be a symptom of oral cancer, particularly if they are persistent, grow, or are accompanied by other symptoms like difficulty swallowing or a lump in the neck.
Leukemia: Certain types of leukemia can cause bleeding gums, mouth sores, or blood blisters due to the abnormal production of blood cells affecting the body's ability to clot blood properly.
Thrombocytopenia: A condition characterized by low platelet count, which can lead to easy bruising and bleeding, including the formation of blood blisters in the mouth.

Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which can lead to easy bruising and bleeding, including in the mouth.
Osler-Weber-Rendu Syndrome (Hereditary Hemorrhagic Telangiectasia): A rare genetic disorder that leads to abnormal blood vessel formation, which can cause bleeding and blood blisters in various parts of the body, including the mouth.
Angina Bullosa Haemorrhagica: A rare condition characterized by the sudden onset of blood blisters in the mouth, often on the soft palate or the inside of the cheeks, without any known cause or systemic disease.