The Strange Reason Your Body Attacks Itself
What scientists are learning about autoimmune diseases
By Ronald Kapper
Picture a security guard who spends years protecting a building, then one night starts locking the residents out of their own apartments. That, in rough terms, is what happens in an autoimmune disease. The immune system, built to hunt viruses and bacteria, turns on the body’s own tissue.
It’s a strange kind of betrayal, and it’s far from rare. Researchers have identified more than 80 autoimmune conditions, including rheumatoid arthritis, type 1 diabetes, multiple sclerosis, lupus, celiac disease, psoriasis, and Hashimoto’s thyroiditis. The National Institute of Allergy and Infectious Diseases notes that these conditions collectively affect a large share of the population, and the Autoimmune Association estimates the number of people living with one in the United States alone runs into the tens of millions. Figures vary depending on which diseases are counted, but nobody disputes that this is one of the most common categories of chronic illness.
So why does the body do it? The honest answer is that science doesn’t have one clean explanation. It has several pieces, and they are starting to fit together.
How the immune system is supposed to work
Your immune system has a hard job: tell “self” from “not self.” Every cell in your body carries molecular markers, and immune cells learn early in life to leave those markers alone.
That training happens mostly in the thymus, a small organ behind the breastbone, where developing T cells are tested. Cells that react too strongly to the body’s own proteins are supposed to be destroyed or switched off. Researchers call this process central tolerance. A second safety net, peripheral tolerance, works out in the tissues and relies partly on specialized regulatory T cells that calm things down.
The system is good, but not perfect. Some self-reactive cells slip through. Most people carry a few of them without ever getting sick, because other checks keep them quiet. Autoimmune disease seems to appear when several of those safeguards fail at once, and something then pushes the dormant cells into action.
That “something” is what researchers have spent decades chasing.
Clue one: your genes load the dice
Autoimmune diseases tend to run in families, though not in a simple way. You don’t inherit lupus the way you inherit eye color. You inherit a tendency.
The strongest genetic signals come from a cluster of genes called the HLA region, which helps immune cells display fragments of proteins for inspection. Certain HLA variants are strongly linked with particular diseases. For example, some are associated with celiac disease and others with type 1 diabetes. Genome-wide studies have since found hundreds of other variants, each nudging risk up or down by a small amount.
Here’s the catch, and it matters for anyone worried about their family history. Identical twins share essentially the same DNA, yet if one twin has an autoimmune disease, the other often doesn’t. Genes load the dice, but they don’t roll them. Something in the environment has to.
Clue two: an infection that leaves a mark
One of the most compelling ideas is called molecular mimicry. Sometimes a germ carries a protein that looks a lot like one of your own. The immune system builds a defense against the invader, then mistakes the lookalike in your tissue for the enemy.
For years this was a plausible theory that was hard to prove. Then came a large 2022 study in the journal Science, led by researchers at Harvard, that followed more than 10 million young adults in the U.S. military. It found that infection with the Epstein-Barr virus, the common virus behind mononucleosis, raised the risk of developing multiple sclerosis dramatically, in the range of 30-fold. People who never caught the virus almost never developed MS. You can read the study abstract in Science.
Keep that in perspective. Epstein-Barr infects the vast majority of adults worldwide, and only a tiny fraction ever develop MS. The virus appears to be a necessary trigger for the disease, not a sufficient one. Other pieces, including genetics, have to be in place. Still, it was among the strongest evidence yet that an ordinary infection can set off a lifelong autoimmune condition years later.
Other candidates are being examined too. Researchers are studying how infections might relate to type 1 diabetes, and how some patients develop autoantibodies after viral illnesses. That research is ongoing, and anyone who tells you the cause of a specific condition is fully settled is getting ahead of the evidence.
Clue three: the gut and its trillions of residents
Roughly 70 percent of immune tissue sits in or near the gut, and it spends every day negotiating with trillions of microbes. That relationship is a big reason scientists have turned their attention to the microbiome.
People with several autoimmune conditions, including rheumatoid arthritis, inflammatory bowel disease, and type 1 diabetes, show differences in their gut bacteria compared with healthy people. What’s not clear yet is the direction of cause. Does a disrupted microbiome help trigger disease, or does the disease change the microbiome? In animal studies, certain bacteria can tip the balance toward inflammation, which suggests at least some causal role. In humans, the picture is murkier.
There’s also the “leaky gut” idea, the notion that a more permeable intestinal lining lets particles into the bloodstream and stirs up immune trouble. Researchers do study intestinal permeability seriously, and it appears altered in some conditions. But the internet version of leaky gut, where it’s blamed for everything and fixed with a supplement, goes well beyond what the evidence supports. If a product promises to cure your autoimmune disease by healing your gut, be skeptical.
Clue four: why women are hit so hard
Here’s one of the most striking patterns in all of medicine. About three out of four people with autoimmune disease are women, according to widely cited estimates. For some conditions, like Sjögren’s syndrome and lupus, the ratio is even more lopsided, with nine women diagnosed for every man in the case of lupus.
Hormones likely play a part. Estrogen tends to strengthen certain immune responses, and many autoimmune conditions first appear or flare during puberty, pregnancy, or the postpartum period. But hormones don’t explain everything. Men with extra X chromosomes (Klinefelter syndrome) have lupus rates closer to women’s than to typical men’s, which points at the chromosomes themselves.
A 2019 line of research from Stanford, published in Cell, offered a clever clue. In female cells, one of the two X chromosomes is mostly silenced, and the process involves a molecule called Xist, which forms clusters with proteins. The researchers found that these clusters can look like targets to the immune system. Male mice engineered to make Xist were more prone to lupus-like disease. It’s a fascinating lead, though it’s early work in animals, and it isn’t the full explanation for the sex gap.
Clue five: modern life
Rates of many autoimmune diseases have risen over the past several decades in industrialized countries, too fast to blame on genetics, which can’t change that quickly. That’s a strong hint that something about how we live matters.
The oldest idea here is the hygiene hypothesis, later reframed as the “old friends” hypothesis. The argument is that our immune systems evolved alongside soil microbes, parasites, and a wider range of bacteria, and that cleaner, more sheltered modern life leaves the immune system under-trained and prone to misfire. It’s a tidy story, and it fits some data, but it can’t explain everything and it doesn’t mean you should stop washing your hands.
Other suspects include:
- Smoking, which is a well-established risk factor for rheumatoid arthritis.
- Low vitamin D levels, linked in observational studies with conditions like MS, though trials of supplements haven’t consistently shown they prevent disease.
- Ultraviolet light, silica dust, and certain solvents, associated with particular conditions.
- Ultra-processed diets and obesity, which promote chronic inflammation and are being studied as contributors.
- Chronic stress, which many patients report before a flare, though proving a causal link is hard.
Notice the pattern: lots of associations, few certainties. That is real science, and I’d rather give you that than a confident list of villains.
Why diagnosis takes so long
If you’ve dealt with an autoimmune disease, you probably know the frustration. Symptoms are often vague and shape-shifting: fatigue, joint aches, low-grade fevers, brain fog, rashes that come and go. Each can have a dozen explanations. Many patients report seeing several doctors over a period of years before getting a name for what’s wrong. Patient advocacy groups often cite an average of around four years, though the exact figure depends on the disease and the study.
Women in particular describe having symptoms dismissed as stress or anxiety, a pattern researchers have documented across many areas of medicine. If something feels persistently wrong, it’s reasonable to keep pushing.
Doctors usually start with blood tests. An antinuclear antibody (ANA) test can flag many autoimmune conditions, though a positive result alone doesn’t prove disease, since a fair number of healthy people test positive. Other tests look for specific autoantibodies, inflammation markers like CRP and ESR, or organ function. Diagnosis often depends on putting symptoms, exam findings, and lab results together, ideally with a specialist such as a rheumatologist, endocrinologist, or neurologist.
Some warning signs worth mentioning to a doctor, especially if they persist beyond a few weeks:
- Unexplained fatigue that doesn’t improve with rest
- Joint pain or stiffness, particularly in the morning
- Recurring rashes or sensitivity to sun
- Unexplained fever
- Numbness, tingling, or vision changes
- Digestive trouble that doesn’t resolve
None of these means you have an autoimmune disease. They mean it’s worth getting checked.
How treatment is changing
For a long time, treatment meant broadly dialing down the immune system with steroids and general immunosuppressants. They work, but they come with real tradeoffs, including a higher risk of infection. The shift of the past two decades has been toward more targeted drugs.
Biologics and targeted therapies. Medications that block specific inflammatory signals, such as TNF or particular interleukins, have transformed rheumatoid arthritis, psoriasis, and inflammatory bowel disease. For many patients, conditions that once led to permanent joint damage are now manageable. Another class, the JAK inhibitors, work from inside the cell and are taken as pills.
Delaying disease before it starts. In 2022 the FDA approved teplizumab (Tzield), the first therapy shown to delay the onset of clinical type 1 diabetes in people at high risk. It doesn’t cure the disease, but buying months or years without insulin dependence is a major change in how doctors think about prevention. The FDA’s announcement explains who it’s intended for.
Resetting the immune system. This is the part that excites many researchers. In CAR-T therapy, originally developed for blood cancers, a patient’s own T cells are engineered to find and destroy B cells, which are the cells that make autoantibodies. A small German group reported striking results in patients with severe lupus, with several going into remission and stopping their other medications. Early reports have since extended to a few other conditions. The numbers are still small, the treatment is expensive and intensive, and long-term safety is being watched closely, so it isn’t an option for most people yet. But it suggests that in some cases the immune system might be rebooted rather than merely suppressed.
Restoring tolerance. Perhaps the ultimate goal is therapies that teach the immune system to stop attacking one specific target while leaving the rest of its defenses intact. Approaches under study include regulatory T cell therapies and antigen-specific treatments. They’re mostly in early trials, so treat any headline promising a “cure” with caution.
What you can do right now
Nobody can promise prevention, because we don’t fully know what causes these diseases. But a few things are reasonable and supported by evidence:
- Don’t smoke, or get help quitting. It’s one of the clearest modifiable risks.
- Talk to your doctor about family history, particularly if relatives have type 1 diabetes, celiac disease, thyroid disease, or MS. Screening is available for some conditions.
- Keep a symptom diary. Dates, triggers, and patterns give a specialist something concrete to work with, and they help when you feel dismissed.
- Stay on your treatment plan if you’ve been diagnosed. Stopping medications because you feel better is a common cause of flares.
- Be wary of miracle claims. No supplement, detox, or restrictive diet has been shown to cure an autoimmune disease. Some dietary changes help certain people with certain conditions, such as strict gluten avoidance in celiac disease, and your care team can tell you what applies to you.
For reliable, plain-language information, the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the Autoimmune Association are good places to start.
Frequently asked questions
Is autoimmune disease contagious?
No. You can’t catch it from another person, though infections may act as triggers in people who are already susceptible.
Can autoimmune diseases be cured?
For most, not yet. Many can be controlled very well, and some people reach long remissions. Research into immune “resets” is promising but early.
If I have one autoimmune disease, am I likely to get another?
It’s more common than chance would predict. People with one condition, such as type 1 diabetes, have a higher chance of developing another, like thyroid disease or celiac disease. That’s one reason regular check-ups matter.
Does stress cause autoimmune disease?
Stress doesn’t appear to be a sole cause, but many patients link flares to stressful periods, and researchers are investigating the connection.
Can children develop autoimmune diseases?
Yes. Type 1 diabetes, juvenile arthritis, and celiac disease often begin in childhood.
Where this leaves us
The old picture of an immune system that simply “goes haywire” is giving way to something more interesting. It looks more like a long chain of small events: a particular set of genes, an infection years earlier, a shift in gut bacteria, a hormonal change, a lifestyle exposure. Any one of them is harmless on its own. Together, in the wrong person, they can tip the balance.
That’s humbling, but also hopeful. Every link in the chain is a possible place to intervene, and for the first time researchers are doing it: delaying diabetes before it starts, resetting immune cells in lupus, and learning which viruses to watch. For the millions living with these conditions, the next ten years of research may matter more than the last fifty.
This article is for general information and isn’t a substitute for professional medical advice. If you’re concerned about symptoms, speak with a qualified healthcare provider.
Sources and further reading:
- Bjornevik K. et al., “Longitudinal analysis reveals high prevalence of Epstein-Barr virus associated with multiple sclerosis,” Science (2022)
- NIAID, NIAMS, and Autoimmune Association resources linked above
- FDA announcement on teplizumab (2022)
Curious about the stranger side of science? Explore more health mysteries, space discoveries, and “what if” questions at What If Science.
