According to the Canadian Journal of Gastroenterology, food-grade hydrogen peroxide can cause damage to the esophagus, duodenum, stomach and airways if consumed at levels high enough to generate caustic injuries. Complications include ulcers, perforations and gastrointestinal erosion. If hydrogen peroxide is accidentally inhaled into the airways, it can narrow the passages between the vocal cords and the trachea or cause the vocal cords to seize and block air flow.
The Canadian Journal of Gastroenterology explains that when hydrogen peroxide is ingested and comes into contact with the metals and enzymes present in a person's organs, it is broken down into water and oxygen. The oxygen released into the body can form apertures in the stomach and small intestines. Dangerously high blood oxygen levels can lead to gas embolisms in the brain, which are similar to the blood clots that cause ischemic strokes.
Food grade hydrogen peroxide is a 35 percent solution, which is much stronger and more caustic than the 3 percent formula that most households purchase at drugstores. The Canadian Journal of Gastroenterology states that the immediate consumption of 500 milliliters or more of water after exposure to hydrogen peroxide ingestion helps to lessen many of the dangerous effects that the substance can cause.
People store 35 percent hydrogen peroxide in their homes as a natural health remedy, but the Canadian Journal of Gastroenterology advises against this due to the health risks it poses. Many of the reported emergency cases related to food grade hydrogen peroxide involved children who accidentally swallowed the liquid.