Anatomy

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How Strong Is the Acid in the Human Stomach?

Last Modified Date: February 15, 2024

The human stomach is a hostile place where hydrochloric acid, potassium chloride, and sodium chloride combine to create a highly acidic brew that breaks down food into easy-to-digest particles. It also defends against pathogens and microbes that could make you ill. On a scale of zero to 14 (from very acidic to alkaline), the stomach’s pH is between 1 and 2. It's just slightly less acidic than battery acid, which can dissolve metal and bone.

Compare that to a vulture that dines on animal carcasses, many of which have been dead for quite a long time. A vulture’s stomach is even more acidic than a human's, with a pH just above 0. There are also two types of bacteria in the bird's stomach – Clostridia and Fusobacteria – to keep vultures from getting sick from the rotting meat.

The strange world of the stomach:

The cells lining the human stomach also release several enzymes and mucus, the latter of which protects the stomach lining from the highly acidic gastric juices and keeps them from damaging the stomach.

The pH level of a human stomach can fluctuate. Some medications and high levels of stress can prevent the body from producing hydrochloric acid. When that happens, the stomach's reactions can range from burping and bloating to heartburn, diarrhea, and nausea.

Vultures will eat “virtually any dead vertebrate – mammal, bird, snake, fish. They prefer recently deceased organisms rather than extremely putrid carcasses,” explains ornithologist Gary Graves of the Smithsonian Institution, adding that “day-old road-killed deer are perfect.”

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