Swallowing your own blood, known as autologous blood ingestion, is a common occurrence. Whether it is harmful depends entirely on the amount ingested. Small quantities are harmless because your body is designed to process and digest them effectively. Adverse symptoms arise only when larger volumes are swallowed, often leading to feelings of illness or discomfort.
The digestive system treats blood similarly to other foods, breaking it down for its nutritional components. The body’s reaction is largely a matter of volume, not toxicity.
Common Routes of Ingestion
Accidentally swallowing small amounts of blood is a frequent event tied to minor injuries or common physical processes. One common scenario is during a nosebleed (epistaxis), where blood trickles down the back of the throat. Medical advice suggests leaning forward during a nosebleed to minimize this backward flow.
Dental procedures are another primary route, especially following a tooth extraction or deep professional cleaning. The slow oozing from a wound in the mouth can mix with saliva and be swallowed unnoticed. Other sources include bleeding gums, a symptom of gingivitis, or minor cuts on the inside of the cheeks or lips. Even a harsh cough can cause minor throat irritation, resulting in a small amount of blood mixed with mucus that is subsequently swallowed.
The Digestive Process of Blood
When blood reaches the stomach, the digestive system immediately begins to break it down like any other protein-rich food. Blood is primarily composed of proteins, notably hemoglobin, the oxygen-carrying molecule in red blood cells. The powerful hydrochloric acid in the stomach begins the denaturation process, unraveling these proteins.
Digestive enzymes then break down hemoglobin into its constituent parts: the protein globin and the iron-containing molecule heme. The globin protein is separated into amino acids, which are absorbed by the small intestine and used by the body for functions like building and repairing tissues. This makes the protein component of swallowed blood harmless and nutritionally useful.
The iron within the heme molecule is also processed for absorption. Heme iron is absorbed intact by intestinal mucosal cells, primarily in the duodenum. While the body has no mechanism to excrete excess iron, iron absorption is tightly regulated. Small amounts of swallowed blood are managed without issue using a specialized system involving the hormone hepcidin to control iron entry into the bloodstream.
When Swallowing Blood Causes Adverse Symptoms
The feeling of sickness associated with swallowing blood is due to irritation of the stomach lining, not a toxic reaction. The presence of blood acts as a physical irritant, triggering nausea. If a significant volume is swallowed, the stomach may attempt to expel the contents, leading to vomiting.
Digested blood can also cause changes in the appearance of vomit and stool. As the iron in the blood is exposed to stomach acid and oxidized, it turns black. If the stomach contents are vomited, the partially digested blood will have a dark, granular appearance, often described as looking like coffee grounds.
If the blood continues through the digestive tract, the oxidized iron compound causes the stool to become dark, sticky, and tar-like, a condition known as melena. While melena can indicate a serious bleed higher up in the gastrointestinal tract, when it follows a known event like a severe nosebleed, it is usually just a sign of the digested, swallowed blood. The characteristic dark color is a direct result of the iron content.
Situations Requiring Medical Attention
While small amounts of swallowed blood are easily managed by the body, certain signs indicate that the underlying bleeding is significant and requires professional medical attention. The most immediate warning sign is the sudden swallowing of a large volume of blood, which can overwhelm the stomach and lead to immediate, forceful vomiting.
Prompt medical evaluation is required if you experience persistent vomiting of blood or vomit that consistently resembles dark coffee grounds, as this may signal an internal gastrointestinal bleed. Symptoms of significant blood loss, including unexplained weakness, dizziness, or lightheadedness, also require attention. The presence of bright red blood in either vomit or stool is a serious symptom, suggesting active, rapid bleeding somewhere in the digestive tract that has not had time to be digested. Medical help should be sought if the bleeding is heavy, persistent, or accompanied by any symptoms of shock.