Most of us don’t give stomach acid a second thought, but some of us are reminded of its power when it leaks into our esophagus and causes heartburn.
The fact that your body contains acid that could burn your skin is pretty impressive, right?
But what is stomach acid, how is it produced, and why doesn’t it destroy our insides?
Here, we’ll answer these questions and more. So get ready to fall in love with your amazing stomach.
What is stomach acid?
Stomach acid is essentially hydrochloric acid.
Scientists measure how acidic something is using the pH scale. This runs from 1–14, with 14 being highly alkaline, 7 being neutral, and 1 being highly acidic.
Stomach acid, also called gastric acid, has a pH of 1–3. So, you wouldn’t want to bathe in it.
Alongside acid, your stomach produces a cocktail of digestive compounds, including enzymes like lipase, which breaks down fat, and pepsin, which breaks down protein.
Together, this heady mixture is called gastric juice. Incredibly, your stomach produces around 17 cups (4 liters) of the stuff each day.
What does stomach acid do?
Stomach acid is a dangerous thing to have sloshing around inside your body, so whatever it’s doing, it must be important.
Stomach acid occurs in nearly all fishes, amphibians, reptiles, birds, and mammals. So, evolutionarily speaking, it’s been around for a very long time. Evolution clearly holds this spicy juice in high regard.
Perhaps stomach acid’s most famous role is helping to break down food before it enters the gut.
It does this directly and also by activating enzymes that chop up compounds in your freshly swallowed lunch.
Stomach acid also helps the body absorb minerals, like magnesium, calcium, and iron, and other nutrients, like vitamin B12.
Although it's best known for its culinary skills, one of stomach acid’s most important jobs is to be a protector.
Guardian of the gut
Bacteria and other pathogens are all around us. They would dearly love to enter our guts and set up shop among our “good” gut bugs.
However, most bacteria don’t like acid. So, any that enter your mouth and end up in your stomach will likely be destroyed.
That’s why people who take heartburn medications for long periods are more prone to infections.
These drugs, such as proton pump inhibitors, reduce the acidity in your stomach. So, bacteria from your mouth can work their way through your less hostile stomach and make it into your gut.
In general, the pH of the stomach stays at or below 4. According to experts, this level is — not coincidentally — “the pH level essential to kill potential microbiological invaders.”
Release the beast
Stomach acid is produced by parietal cells, which sit in pits in your stomach lining. And because this colorless fluid is dangerous, your body controls its release very carefully.
It can’t just flow freely all day. Stomach acid needs to be released at the right time.
The brain has a direct link to the stomach through the vagus nerve. When you’re expecting to eat or simply smell some delicious muffins, your brain sends a message to your stomach to release a hormone called gastrin.
Gastrin helps trigger the release of gastric acid.
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Gastrin is also released in response to certain components entering your stomach — particularly protein. And when your stomach is full, its walls stretch, and this also triggers gastrin’s release.
Alongside gastrin, a wide range of other compounds and hormones make sure stomach acid is pumped out at the right time. These include histamine and ghrelin, the so-called hunger hormone.
Why doesn’t the stomach digest itself?
As we've mentioned, your brain, hormones, and other messengers keep a tight rein on your stomach acid. But it’s still released multiple times a day, so how does your stomach not get digested?
Your body keeps your gut safe in several other ways.
For example, mucus cells in your stomach produce mucus and bicarbonate. They line the stomach's wall and keep it at a near-neutral pH.
And scientists are still uncovering other compounds that help keep your stomach from digesting itself.
Some of these lesser-known actors are prostaglandins, a group of lipids that help repair damaged tissues and have a range of other jobs. Scientists now think that they also help protect the stomach from itself.
Other protective chemicals may include:
Nitric oxide: This gas acts as a biological messenger and may inhibit gastric acid secretion.
Hydrogen sulfide: This gas also acts as a messenger. There's evidence that it can reduce pH in the stomach and increase the amount of protein in the mucus lining.
Overall, scientists have identified a whole host of compounds that can help dial up or down the amount of gastric acid in your stomach.
Exactly how your stomach makes sense of these competing molecules is still being thrashed out, however.
Aside from this incredible selection of signals, your stomach has other defenses, too.
For instance, the cells that line your stomach are tough — they're surprisingly resistant to acid, compared with cells elsewhere in your body. So, even if they are exposed to the acid, they can survive longer than most cells would.
And if all of the above fails, the lining of your stomach is excellent at repairing itself swiftly. The whole internal lining of the stomach is replaced every 2–4 days.
All hail stomach acid
We hope, if nothing else, that this article has given you a new love for your stomach and its acid.
Not only can stomach acid help you digest food and absorb nutrients, it can also help fend off microbes that want to make you sick.
So, next time you have one of those burps where you feel a bit of acid coming up, don’t grimace; smile. But if the problem persists, make sure you talk with your doctor.
Association between proton pump inhibitor therapy and Clostridium difficile infection in a meta-analysis. Clinical Gastroenterology and Hepatology. (2012). https://www.sciencedirect.com/science/article/abs/pii/S1542356511010780
Association of long-term proton pump inhibitor therapy with bone fractures and effects on absorption of calcium, vitamin B12, iron, and magnesium. Current Gastroenterology Reports. (2010). https://pubmed.ncbi.nlm.nih.gov/20882439/
Calcitonin gene-related peptide: Physiology and pathophysiology. Physiological Reviews. (2014). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4187032/
Gastric acid in vertebrates. Scandinavian Journal of Gastroenterology. (1992). https://pubmed.ncbi.nlm.nih.gov/1290053/
Gastric mucosal defence mechanisms: A brief review. Scandinavian Journal of Gastroenterology. (1988). https://pubmed.ncbi.nlm.nih.gov/3072665/
Gastrin. (2021). https://www.yourhormones.info/hormones/gastrin/
How does the stomach work? (2016). https://www.ncbi.nlm.nih.gov/books/NBK279304/
Infusion of a novel peptide, calcitonin gene-related peptide (CGRP) in man. Pharmacokinetics and effects on gastric acid secretion and on gastrointestinal hormones. Regulatory Peptides. (1985). https://www.sciencedirect.com/science/article/abs/pii/016701158590013
Prostaglandins. (2019). https://www.yourhormones.info/hormones/prostaglandins/
Prostaglandins, NSAIDs, and gastric mucosal protection: Why doesn't the stomach digest itself? Physiological Reviews. (2008). https://journals.physiology.org/doi/full/10.1152/physrev.00004.2008
Role of nitric oxide in the gastrointestinal tract. Arthritis Research and Therapy. (2008). https://arthritis-research.biomedcentral.com/articles/10.1186/ar2465
The apical surface of canine chief cell monolayers resists H+ back-diffusion. Nature. (1985). https://www.nature.com/articles/313052a0
The phylogeny and biological function of gastric juice — microbiological consequences of removing gastric acid. International Journal of Molecular Sciences. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6928904/
The physiology of the gastric parietal cell. Physiological Reviews. (2020). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7327232/
The role of hydrogen sulfide in gastric mucosal damage. Medical Gas Research. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6607860/