Sudden blood packets inside the mouth is usually the appearance of blood blisters, the possible causes are trauma, blood diseases, viral infections, etc., as follows. 1. trauma: oral mucosal blood blisters caused by trauma, often have a clear history of trauma, such as bites, eating too hard and too hot food. 2. Blood diseases: some patients with blood diseases have oral symptoms in addition to systemic symptoms, such as acute sudden or secondary thrombocytopenic purpura can appear in the oral cavity hemorrhagic blisters. 3. viral infections: trigeminal herpes zoster patients can appear blood blisters when the condition is serious, patients with epidemic hemorrhagic fever oral soft palate, pharynx can appear spot bleeding or blood blisters. There may be other reasons for the appearance of blood blisters in the oral cavity, it is recommended to go to the hospital in time.