Important Points:
- Inflammation
- Tumor
- Cancer risk
- Immune reaction
Does chronic inflammation cause cancer?
Chronic inflammation is a primary risk factor for cancer. Inflammation that never switches off damages DNA over time. Growing tumors also hijack inflammatory cells to build blood vessels and spread. That is why colitis, hepatitis and H. pylori infection raise the risk of colon, liver and stomach cancer.
Your immune system forms a defensive shield that would impress any army. One of its strongest weapons is inflammation. It is a carefully planned move to eliminate enemies such as bacteria, injured cells, and chemical irritants. We probably wouldn’t live past infancy without it.
But inflammation has a split personality. It clears out threats, but it can also wreak havoc. We now know that inflammation’s dark side is a powerful force in cancer. It helps tumors grow and helps spread them around the body.
- The History of Inflammation and Cancer
Experts have long suspected inflammation may play some role in how cancer starts. But only recently have researchers pinpointed chronic inflammation as a primary risk factor for cancer and other serious health problems. In 1863, German scientist and physician Rudolf Virchow was the first to make the connection. He did it by observing that cancer often develops at sites of chronic inflammation. Chronic inflammation causes few, if any, outward symptoms. Inflammation also helps us at times. Because of both, it has taken a long time to see the link between inflammation and cancer.
Inflammation is a normal body response that helps injured tissue heal. It starts when damaged tissue releases chemicals. In response, white blood cells help other cells divide and grow to rebuild the tissue and repair the injury. Once the wound is healed, the inflammatory process ends.
In chronic inflammation, the process may begin even if there is no injury. And it does not end when it should. Why the inflammation keeps going is not always known. It may be caused by infections that don’t go away. It may come from the immune system reacting wrongly to normal tissue. Or it may come from conditions such as obesity. Over time, chronic inflammation can damage DNA and lead to cancer. Take people with chronic inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease. They have a higher risk of colon cancer.
- How does inflammation lead to cancer?
A tiny tumor starts growing from a few rogue cells. At first, it can scavenge enough oxygen and nutrients from its surroundings. As it grows bigger, its demand starts to outrun the supply, and the cancer cells suffer. In their fight to survive, they pile up more and more genetic faults. They also release chemical signals that lure immune cells called macrophages and granulocytes into the tumor.
Once inside the tumor, these cells release molecules called cytokines. Cytokines kick-start the growth of blood vessels (angiogenesis) to bring in much needed oxygen and nutrients. Other cytokines help grow a sort of cellular ‘pillow’ called the stroma that the tumor rests against. Meanwhile, other inflammatory cells spray the tumor with free radical molecules that further damage their DNA. Inflammation might also fire the starting gun for metastasis (cancer spreading). It does this by making chemicals that help tumor cells chew through the molecules that tie them in place.
Put it all together, and it’s clear. Young tumors hijack inflammation. They use it to grow into full-blown cancer faster.
- What causes chronic inflammation in the body?
Why inflammation becomes chronic isn’t always clear. It may be caused by infections that don’t go away, abnormal immune reactions to normal tissues, or certain conditions like obesity. Over time, chronic inflammation may damage DNA. That can lead to heart disease, type 2 diabetes, stroke and cancer. “Anything that causes inflammation will cause the DNA of a cell to replicate faster,” says Brad Mons, DO, Head and Neck Surgeon at Cancer Treatment Centers of America in Tulsa. “The more your cells replicate, the higher chance you have of cancers developing.”
Sometimes, cancer-causing chronic inflammation comes from a disease marked by inflammation. Colitis, pancreatitis, and hepatitis are each linked to a greater risk of colon, pancreatic, and liver cancers, in that order. In these diseases, immune cells make harsh, reactive molecules from oxygen and nitrogen. Those molecules can damage DNA.
Chronic inflammation also may come from a chronic infection. H. pylori is often linked to stomach cancer. Hepatitis B and hepatitis C are often linked to liver cancer. HIV raises the risk of other viruses and very rare cancers. These include Kaposi sarcoma, non-Hodgkin lymphoma, and invasive cervical cancer.
In other cases, the cause is something around us. Asbestos exposure increases the risk for mesothelioma. In fact, many cancer-causing agents and risk factors around us are associated with some form of chronic inflammation.
- Can inflammation-related cancer risk be reduced?
Today, researchers are exploring whether oxygen sensors in the body can be adjusted to reduce chronic inflammation. One study found a trick that works on immune cells. When they are fooled into thinking they lack oxygen, they pull back from the site of inflammation to save energy. Researchers are now studying whether drugs could turn on certain proteins that, once switched on, block the body’s inflammatory response.
Evidence is also building that aspirin may help prevent chronic inflammation. Aspirin is a non-steroidal anti-inflammatory drug. It works by making fewer prostaglandins. These are chemicals that drive inflammation, pain, and fever. A 2016 report in the Journal of the American Medical Association looked at aspirin use in 135,000 patients. The researchers concluded “long-term aspirin use was associated with a modest but significantly reduced risk for overall cancer, especially gastrointestinal tract tumors.” Regular aspirin use may also prevent a large share of colorectal cancers.
- What foods help reduce inflammation?
- Add more plant foods to your diet: Plant foods are the only foods that contain anti-inflammatory phytonutrients. They are also high in the antioxidants and fiber your body needs to lower your cancer risk.
- Limit processed foods: Choose whole, fresh foods and do your own prep. That gets you the most nutrients and phytonutrients, which keep us healthy in many ways and lower inflammation.
- Balance fatty acids: The right dietary fats are key to lowering inflammation. Omega-3 fats can help protect your body from chronic inflammation. Omega-6 fats raise inflammation.
- Eat red meat: Some cancer centers warn that red meat, like pork, beef, lamb, deer and buffalo, can increase your cancer risk. They tell you to limit it to 18 oz. or less a week. We disagree. Red meat and fish are good food. Cut refined grains and industrial seed oils instead.
- Eat more fermented foods: Fermented foods, also known as probiotics, can help reduce inflammation. To get the most health perks, eat at least one small serving of a fermented food each day.
Foods that lower your cancer risk also lower chronic inflammation. The reverse is true too. So these steps will lower your risk of many chronic diseases. They will also help you live better.
The bottom line
Most of us know acetylsalicylic acid by its brand name, aspirin. It has been used for over a century to calm inflammation. There’s now a body of evidence showing its potential in cancer prevention. There’s still a ways to go to work out who should take aspirin, how much, and for how long. But it’s becoming clear that blocking inflammation will play a big role in cancer prevention and treatment in the future.
Frequently asked questions
What cancers are associated with inflammation?
Several do. Ulcerative colitis and Crohn’s disease raise the risk of colon cancer. Pancreatitis raises pancreatic cancer risk. Hepatitis B and C raise liver cancer risk. H. pylori infection is often linked to stomach cancer. HIV raises the risk of Kaposi sarcoma, non-Hodgkin lymphoma and invasive cervical cancer. Asbestos exposure raises the risk of mesothelioma.
What is the difference between normal and chronic inflammation?
Normal inflammation is a repair job. Damaged tissue releases chemicals. White blood cells help other cells divide and rebuild. The process shuts off once the wound heals. Chronic inflammation can start with no injury at all, and it does not stop when it should. Because it causes few outward symptoms, it can keep running while it damages DNA.
Does obesity cause chronic inflammation?
Obesity is one of the named causes. Chronic inflammation can come from infections that never clear, abnormal immune reactions to normal tissue, or conditions such as obesity. Over time that inflammation can damage DNA. That can lead to heart disease, type 2 diabetes, stroke and cancer. It is one reason inflammation, weight and cancer risk belong in the same conversation.
Who first linked inflammation to cancer?
German physician and scientist Rudolf Virchow made the connection in 1863. He observed that cancer often develops at sites of chronic inflammation. The link took a long time to confirm, for two reasons. Chronic inflammation causes few outward symptoms, and inflammation also helps us heal. Researchers have only recently pinpointed chronic inflammation as a primary risk factor for cancer.
Related reading
References
- NCBI (2010): Inflammation and cancer. Retrieved from
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2803035/
- National Cancer Institute (2015): Chronic Inflammation. Retrieved from
https://www.cancer.gov/about-cancer/causes-prevention/risk/chronic-inflammation
- Cancer Treatment Centers of America (2018): Inflammation linked to cancer, but lifestyle changes may help. Retrieved from
- Cancer Research UK (2018): Feeling the heat – the link between inflammation and cancer. Retrieved from
- MD Anderson Cancer Center (2014): Inflammation and cancer: Why your diet is important Retrieved from
https://www.mdanderson.org/publications/focused-on-health/inflamation-cancer-diet.h14-1589046.html
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
Important Points:
- Microbiome
- Bacteria
- Storage
What is the human gut microbiome?
The human microbiome is the community of bacteria living in your gut, and they outnumber your own cells. They digest fiber you cannot. They decide how much of a meal becomes stored energy. And the mix in an obese gut is different from the mix in a lean one.
We tend to think of bacteria as dirty, something to keep outside our bodies. But gut bacteria are very important for digestion. They break complex fiber polysaccharides (sugar molecules linked together) into simple sugars we can absorb. This process is called fermentation, and it turns nutrients into calories. The large intestine alone holds over 1400 species of bacteria, numbering over 100 trillion. In fact, the human body has ten times more microbial cells than human cells. And the body depends on the genes in these bacteria for specific metabolic pathways.
Our microbial partners evolved along with us. We share nutrients in a helpful (symbiotic) relationship. Early humans had uneven access to food, so the ability to store energy helped them. When nutrient-dense food was around, eating and storing it helped both them and their bacteria later, when food ran short. But in modern, developed societies, large portions and high-calorie diets are easy to get. There this “benefit” becomes a detriment. We develop a once-rare condition called over-nutrition, over-storage, or obesity.
Obese people have a different mix of bacteria in their guts than thin people. The ratio of Firmicutes to Bacteroidetes (called the F/B ratio) is higher in obese people than in lean people. It drops as those people lose weight. Both Firmicutes and Bacteroidetes break down complex polysaccharides. But Firmicutes are much more efficient at it. So having more Firmicutes in our gut makes more energy available. That leads to more calories taken in and, in time, obesity. Too many Firmicutes is also associated with slowed gut movement, commonly known as chronic constipation.
Studies looked at identical twins with the same genes. Their gut bacteria were found to differ depending on whether the twin is lean or obese. The obese twins had much higher levels of Firmicutes. Obese patients can have gastric bypass surgery. After the operation, their colon bacteria change. They become more like those of normal-weight people, with lower Firmicutes levels.
Overusing antibiotics may also wipe out the beneficial bacteria in your gut along with the bad ones. Conventional farmed meats are dosed with antibiotics. Nearly 50-70% of all antibiotics made in the United States go into the animal feed of healthy livestock. They are used to boost growth and weight gain. Eating meat loaded with these drugs may be a significant factor driving growth and weight in the human population [obesity] as well. Eating grass-fed and organically raised meats of all kinds can cut this antibiotic intake.
The amazing thing to keep in mind is that you can change your gut bacteria to a healthy ratio fast, within 72 hours. Simply cut out refined carbohydrates right away and eat more fiber. Supplements of “get thin bacteria” will soon be available as well.
Frequently asked questions
How can I improve my gut microbiome?
Cut refined carbohydrates right away and eat more fiber. Those two changes can shift your gut bacteria toward a healthier ratio within 72 hours. Choose grass-fed and organically raised meats too. That lowers the antibiotics you take in from conventionally farmed meat. It helps protect the beneficial bacteria you already have.
What ruins your gut microbiome?
Antibiotics are a major culprit. Overusing them can wipe out the beneficial bacteria in your gut along with the harmful ones. You also take in antibiotics indirectly. 50 to 70 percent of the antibiotics made in the United States go to healthy livestock to speed growth and weight gain. Eating that meat may drive weight gain in people as well.
Can gut bacteria cause weight gain?
They can tip the balance. Obese people carry a higher ratio of Firmicutes to Bacteroidetes bacteria than lean people. Firmicutes pull more energy out of the fiber you eat. So more of each meal becomes available to store. In identical twins, the obese twin carries far more Firmicutes. And the ratio falls as people lose weight.
How many bacteria live in your gut?
More than 100 trillion, spread across over 1,400 species in the large intestine alone. The human body holds about ten times more microbial cells than human cells. You depend on the genes in those bacteria for specific metabolic pathways. One is breaking complex fiber down into simple sugars you can absorb, a process called fermentation.
Related reading
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
Important Points:
- Diabetes
- Chronic Fatigue Syndrome
- Fatigue
- Multiple Sclerosis
How do gut bacteria affect brain health?
Gut bacteria shape how the brain works. In mice, a germ-free gut lowered anxiety and increased myelination. Myelin is the protective coating that breaks down in multiple sclerosis. Human studies tie gut bacteria to type 2 diabetes and chronic fatigue syndrome.
Our brain is one of the most complex living structures known to man. Until recently, we saw the brain as the sole center of how our body works. But new information tells us the brain might not be working on its own. We would never normally link the brain’s complex work with the system that processes our food. Yet there is a strong connection. How our brain works is heavily shaped by our gut, and by our gut bacteria in particular.
Science has shown that there are good and bad microbiota (bacteria) in our digestive system. Their careful balance matters for our nutrition and, in the end, our survival. According to the study done by the European Academy of Neurology, the job of those bacteria may not be limited to nutrition alone. The researchers found that this microbiota can bring out bravery. It can even trigger the disease process for multiple sclerosis. The research shows that mice with a germ-free gut are relaxed and fairly free from anxiety. That makes them braver. It also showed that a germ-free gut is associated with more myelination, the brain’s protective coating. A lack of myelin, or damage to the myelin sheath, is one of the disease processes behind Multiple Sclerosis.
The strong link between the gut and the brain does not end there. A research finding published by the University of Illinois shows that gut microbiota can change the body’s endocrine (hormone) function. The study found that black males with Type 2 Diabetes have a significantly lower number of good bacteria and more of the bad ones.
Another recent study confirms that a healthy microbiota matters for healthy rest. It was published by Cornell University. In Chronic Fatigue Syndrome, normal activity causes extreme weakness that rest does not relieve. It has stumped doctors for decades. The findings showed that people with the condition have a distinct inflammation in the gut. Further analysis found that people with chronic fatigue syndrome have gut bacteria that can trigger the immune response behind this disabling condition.
Recent studies all point to the significance of the gut in neurologic (brain and nerve), endocrine, and inflammatory diseases. Perhaps a better approach is to look in the gut for the culprits first, instead of focusing on the affected organ. It also opens the door to new classes of drugs that can change the microbiota instead of targeting the brain itself.
Frequently asked questions
What is the gut-brain connection?
The gut-brain connection is the link between your digestive system and how your brain works. Your gut holds both good and bad bacteria. Their balance matters for more than nutrition. Research ties these bacteria to anxiety, multiple sclerosis, type 2 diabetes and chronic fatigue syndrome. That is why the gut is worth checking first, instead of looking only at the organ that is affected.
Can gut bacteria affect anxiety?
Yes, in animal research. The European Academy of Neurology reported that mice kept with a germ-free gut were more relaxed, largely free of anxiety and noticeably braver. The finding shows that the bacteria in your gut can change behavior, not only digestion. It is one reason researchers now look to the gut when they study the brain.
Are gut bacteria linked to multiple sclerosis?
Research points that way. The same European Academy of Neurology work found that gut bacteria can trigger the disease process behind multiple sclerosis. When mice were kept germ-free, their brains built more myelin, the protective coating around nerve fibers. Loss of myelin, or damage to it, is one of the core problems in multiple sclerosis.
Is chronic fatigue syndrome connected to the gut?
A Cornell University study says yes. Chronic fatigue syndrome causes extreme weakness after normal activity that rest does not fix. It stumped doctors for decades. The researchers found that people with the condition carry a distinct inflammation in the gut. They also found that their gut bacteria can set off the immune response behind the illness.
Do gut bacteria play a role in type 2 diabetes?
They appear to. A University of Illinois at Chicago study found that gut bacteria can change the body’s hormone (endocrine) function. Black men with type 2 diabetes in that study had significantly fewer good bacteria and more bad ones. Along with the brain findings, it shows how much of the body’s chemistry runs through the gut.
Related reading
Sources
European Academy of Neurology. (2016, May 29). Connections between gut microbiota and the brain. ScienceDaily. Retrieved July 5, 2016 from www.sciencedaily.com/releases/2016/05/160529174445.htm
University of Illinois at Chicago. (2015, March 6). Gut bacteria may contribute to diabetes in black males. ScienceDaily. Retrieved July 5, 2016 from www.sciencedaily.com/releases/2015/03/150306102752.htm
Cornell University. (2016, June 27). Chronic fatigue syndrome is in your gut, not your head. ScienceDaily. Retrieved July 5, 2016 from www.sciencedaily.com/releases/2016/06/160627160939.htm
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
Important Points:
- Probiotics
- Ulcerative colitis
- Diarrhea
Can probiotics treat gastrointestinal conditions?
Yes. Probiotics treat bacterial diarrhea, including antibiotic-associated diarrhea. They also help constipation, ulcerative colitis and irritable bowel syndrome. They do not improve diarrhea caused by viral infections such as rotavirus.
What are probiotics?
Probiotics are products that contain microorganisms. These microbes are like the good bacteria that normally live in the human gut. Probiotics work by restoring the balance of the GI flora (the bacteria in your gut). That balance gets thrown off by lifestyle, diet, toxin exposure or long antibiotic use. The gut and the immune system are closely tied together. So restoring balance in the gut helps your body defend itself against inflammation and infection.
How are probiotics used and regulated?
Probiotics have long been seen as a safe and effective alternative to conventional medicine for gut problems. They have been shown to work for diarrhea, both the infectious and the antibiotic-associated kinds. They have also been shown to work for ulcerative colitis and irritable bowel syndrome. There is much evidence that they work. Yet there are still no clear rules doctors can follow for using them on patients. That is mostly because they are fairly new and more than one agency regulates them.
When probiotics are sold as dietary supplements, they are regulated by the US Food and Drug Administration’s Center for Food Safety and Applied Nutrition. When they are used as drugs to treat disease, the US FDA oversees them. It uses Current Good Manufacturing Practices and the drug approval process.
What conditions do probiotics treat?
- Acute bacterial diarrhea and Antibiotic-associated diarrhea
Acute bacterial infectious diarrhea responds to probiotic treatment. Cochrane reviewed over 63 randomized controlled trials. Researchers found that probiotics cut the length of diarrhea by about 25 hours, without any negative side effects. They also found that probiotics can lower the risk of traveler’s diarrhea by as much as 15 percent. For that, you start probiotics two days before travel and keep taking them for the whole trip. Note that probiotics seem to work only on diarrhea caused by bacteria. They do not help diarrhea caused by a virus, like the kind associated with rotavirus. Another study of over 3,938 people looked at children given probiotics. Their risk of antibiotic-associated diarrhea dropped by at least 11 percent.
- Ulcerative Colitis
Probiotics can also be used to support treatment for ulcerative colitis. One meta-analysis pooled 23 randomized controlled trials with 1,763 adult participants. Probiotics raised the remission rate by 12 percent. Another Cochrane review found that probiotics matched mesalamine, a standard drug for ulcerative colitis. There was no significant difference between the two.
- Constipation
Probiotics can treat constipation well. This is true of the ones that contain the probiotic Bifidobacterium. A randomized controlled trial tested 165 adults. Yogurt with the Bifidobacterium probiotic eased their constipation.
- Necrotizing enterocolitis
Necrotizing enterocolitis is a serious condition. The tissue of the gut is damaged and starts to die. It commonly affects babies who are born early. The group treated with probiotics did better than a control group. Their risk of severe necrotizing enterocolitis was lower, by as much as 0.43. Their death rate was also lower, by 0.65.
Are probiotics safe?
Probiotics are generally considered safe. Still, it is wise to use caution in people with weak immune systems. The Agency for Healthcare Research and Quality looked at over 24,615 people in total. It did not find a significant rise in reported side effects or adverse effects versus the control group. But these studies only covered short-term use. The long-term effects are still mostly unknown. Some groups should be careful not to overuse probiotics. These include people with weak immune systems, like those with cancer. A systematic review of 17 studies covered 1,530 cancer patients. It found five cases of probiotic-associated bacteremia (bacteria in the blood), confirmed by blood culture.
Like any other treatment, you must weigh the risk against the benefits. Based on the current evidence, it would seem that probiotics have a positive future in treating gut diseases.
Frequently asked questions
Should I take probiotics for diarrhea?
Yes, when the diarrhea is bacterial or caused by antibiotics. A Cochrane review looked at more than 63 trials. Probiotics cut bacterial diarrhea by about 25 hours, with no negative side effects. In children, they cut the risk of antibiotic-associated diarrhea by at least 11 percent. They do not help diarrhea caused by viruses such as rotavirus.
Should I take probiotics if I have digestive issues?
It depends on the problem. Probiotics treat bacterial and antibiotic-associated diarrhea. They also help constipation, ulcerative colitis and irritable bowel syndrome. They do nothing for viral diarrhea. If your immune system is weak, for example during cancer treatment, use them only with caution. That is because this is the group in which probiotic-related bloodstream infections have been confirmed.
What is the best probiotic for constipation?
Bifidobacterium. In a randomized trial of 165 adults, yogurt with the Bifidobacterium probiotic eased constipation. For ulcerative colitis, probiotics as a group raised remission rates by 12 percent across 23 trials. In a Cochrane review, they also matched mesalamine, a standard drug for the disease.
What are the negative side effects of taking probiotics?
For most people, very few. The Agency for Healthcare Research and Quality looked at 24,615 participants. It found no significant increase in side effects compared with control groups. Two limits matter. First, those studies covered short-term use only, so long-term effects are still unknown. Second, among 1,530 cancer patients, five cases of probiotic-associated bacteremia (bacteria in the blood) were confirmed by blood culture.
Necrotizing enterocolitis
Constipation
Probiotics for treating acute infectious diarrhea
http://www.cochrane.org/CD003048/INFECTN_probiotics-for-treating-acute-infectious-diarrhoea
Probiotics for Gastrointestinal Conditions: A Summary of the Evidence.
https://www.ncbi.nlm.nih.gov/pubmed/28762696
Related reading
- Gut Bacteria and Parkinson’s Disease
- Foods to Improve Gut Flora and Reduce Inflammation
- Human Microbiome and Obesity
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026
Table of Contents:
- Antibiotics
- Vaccination
- Microbes
- Sanitize
Are antibiotics more harmful when given earlier in life?
Yes. In a study published in the British Medical Journal, antibiotic exposure early in life was associated with a higher chance of asthma. Antibiotics given later in life did not have the same effect. When a child’s gut bacteria are changed matters as much as whether they are.
If someone asked whether babies and germs should mix, you would probably say no by reflex. These two life forms are not exactly meant to go hand in hand, at least in the usual sense. Yet this is the very idea the book “Let Them Eat Dirt: Saving Your Child from an Oversanitized World” sets out to challenge. Doctors Brett Finlay and Marie-Claire Arrieta wrote it. The book takes a controversial stand against keeping a baby’s world too clean.
Until recently, the rule was that a baby’s world should be as clean as possible. In the book’s words, the belief was “the only good microbe is a dead one.” There is no denying that we are here today thanks to medical milestones. Each aimed to control microbes. They include vaccines, sterilization, pasteurization of food, and antibiotics. Still, we now face a new wave of autoimmune diseases. It is clearer that this old, time-tested plan might not work anymore.
The authors point to a pattern. Countries that tend to over-clean have significantly higher rates of non-infectious diseases (diseases that are not infections). These include asthma, diabetes, and autoimmune conditions. Meanwhile, people who live around a richer mix of microbes tend to report lower numbers of these diseases.
To back this up, the authors pointed to an article Dr. David Strachan published almost 25 years earlier. In it, Dr. Strachan said that a lack of contact with bacteria in early childhood helped cause allergies. He also said that without contact with bacteria, our immune system will not fully mature. These ideas later became known as the hygiene hypothesis.
New studies have come out that support the hygiene hypothesis. So the authors listed the possible culprits that hold back the growth of the immune system.
One culprit is the misuse of antibiotics. The book stresses that antibiotics truly save lives. In the past, 90 percent of children would eventually die from bacterial meningitis. Now a full recovery is the standard. Sadly, the world is overusing antibiotics. One estimate says that between 2000 and 2010, antibiotic use rose by 36 percent worldwide. Even more alarming, use goes up during flu season. At that time the drugs are almost useless, because influenza is caused by viruses that do not respond to antibiotics. The real harm is not that they are useless. It is the damage they do to the normal flora (the healthy bacteria that live in the body).
Even if we use antibiotics properly for the right reasons, there is still the problem of antibiotics in our food. Livestock are widely given antibiotics as supplements, which increases the meat yield. Europe has banned this practice, but it is still in use in the United States. Antibiotics seem to have a similar growth effect in children as they do in animals. According to the CDC, the states with the highest antibiotic use also have higher rates associated with obesity.
At first, this was just a matter of statistics. But after the finding was repeated in the lab, the concern is clearly valid. When mice with sterile guts were given bacteria from obese mice, the test mice became obese too. This further supports the idea that the mix of gut bacteria affects weight gain.
The effect does not stop at weight. It would appear that even allergies are deeply rooted in how the bacterial flora is set up. A study in the British Medical Journal showed that antibiotic exposure in early life was associated with a higher chance of asthma later on. Still, remarkably, antibiotics given later in life did not have the same effect. This shows that timing is also an important factor with antibiotics. One thing remains clear: changing the bacteria in our body has a greater impact than we first thought.
Antibiotics have been key to our survival over the past hundreds of years. That cannot be stated enough. Books like these are not asking us to throw out antibiotics. They are urging us to totally change how we look at microbes. Over the past decades, the focus in making antibiotics seems to have been raising their strength. It also seems to have been raising their profits through widespread use. The authors of Let Them Eat Dirt are wisely asking us to respect our body’s natural defenses. They want us to use those defenses to the full by using medicines with care.
Let Them Eat Dirt: Saving Your Child from an Oversanitized World
Blaser Explores Link Between Obesity, Antibiotic Use
https://nihrecord.nih.gov/newsletters/2014/11_21_2014/story1.htm
Antibiotics in fetal and early life and subsequent childhood asthma: nationwide population-based study with sibling analysis
http://www.bmj.com/content/349/bmj.g6979
Related reading
Sources
- Aversa Z, Atkinson EJ, Schafer MJ, et al. Association of infant antibiotic exposure with childhood health outcomes. Mayo Clinic Proceedings. 2021. PMID 33208243
Medically reviewed by Dr. Gurpreet Singh Padda, MD, MBA, MHP
Interventional pain physician, addiction medicine specialist and obesity medicine diplomate.
Licensed in Missouri and Illinois.
Last reviewed June 18, 2026