Celiac disease is caused by an immune reaction to gluten, but that reaction only happens when several factors collide: specific genes, a trigger that activates the immune system, and changes in the gut lining that allow gluten fragments to reach immune cells they’d normally never encounter. About 1% of the global population has celiac disease, and while gluten is the substance that does the damage, the reasons some people develop the condition and others don’t involve a deeper chain of causes.
Genetics Set the Stage
Nearly every person with celiac disease carries one of two gene variants that control how the immune system identifies threats. About 90% of celiac patients carry the HLA-DQ2 variant, roughly 5% carry HLA-DQ8, and most of the remaining 5% carry at least a partial copy of one of these genes. In Europe, fewer than 0.5% of celiac patients lack both variants entirely. These genes code for proteins on the surface of immune cells that act like docking stations, grabbing fragments of digested food and presenting them for inspection. In people with DQ2 or DQ8, those docking stations happen to fit gluten fragments particularly well.
Carrying these genes doesn’t guarantee you’ll develop celiac disease. Up to 40% of the general population carries DQ2 or DQ8, yet only a fraction ever develops the condition. The genes are necessary but not sufficient on their own, which is why researchers focus heavily on the environmental triggers that tip genetically susceptible people into active disease.
How Gluten Triggers the Immune System
When you eat wheat, barley, or rye, your digestive system breaks gluten down into smaller protein fragments called peptides. Most of these pass through the gut harmlessly. In celiac disease, certain gluten peptides resist full digestion and make their way through the intestinal lining into the tissue underneath. Once there, a natural enzyme in your body modifies these peptides chemically, converting one amino acid (glutamine) into another (glutamic acid). This small change is critical: it reshapes the peptide so it locks perfectly into those DQ2 or DQ8 docking stations on immune cells.
Once an immune cell presents the modified gluten fragment, a specific type of white blood cell recognizes it as a threat and launches an inflammatory attack. This inflammation damages the finger-like projections (villi) that line the small intestine and absorb nutrients. Over time, the villi flatten, reducing the intestine’s ability to absorb iron, calcium, vitamins, and other essential nutrients. The immune system also produces antibodies against both gluten and the body’s own enzyme that modified it, which is why celiac disease is classified as autoimmune.
The Gut Barrier Breaks Down First
For gluten peptides to reach immune cells beneath the intestinal lining, they first need a way through that lining. The cells of your intestinal wall are held together by tight junctions, essentially molecular locks that control what passes between cells. In celiac disease, gluten itself triggers the release of a protein called zonulin, which loosens those locks and increases intestinal permeability.
Research from the American Academy of Pediatrics found that children who went on to develop celiac disease showed a significant rise in zonulin levels an average of 18 months before their diagnosis. This suggests the gut barrier starts breaking down well before symptoms appear, creating a window where more and more undigested gluten fragments slip through to the immune system. The same study found that antibiotic use accelerated this process: children exposed to more than three courses of antibiotics had a faster rate of zonulin increase before disease onset.
Viral Infections Can Flip the Switch
One of the more striking discoveries in celiac research involves reovirus, a common and usually harmless intestinal virus that most children encounter in early life. In genetically susceptible individuals, reovirus infection appears to reprogram the immune system’s response to dietary proteins like gluten.
Normally, the immune system learns to tolerate food proteins through a process involving regulatory immune cells that signal “this is safe, ignore it.” Reovirus disrupts this tolerance process in two ways: it suppresses the creation of those regulatory cells, and it simultaneously promotes an aggressive inflammatory response to dietary proteins. In mouse models carrying the celiac-associated gene, reovirus infection triggered a loss of oral tolerance to gluten, activating the same enzyme involved in celiac disease in more than 60% of infected animals. Human data supports this connection. Celiac patients tend to have higher antibody levels against reovirus, and those with the highest levels show greater signs of the inflammatory pathway in their intestinal tissue.
Conditions That Raise Your Risk
Beyond genes and environmental triggers, certain conditions are strongly associated with celiac disease. About 6% of people with type 1 diabetes have biopsy-confirmed celiac disease, likely because both conditions share genetic risk factors in the same region of the immune system’s genetic code. People with Down syndrome face a similar risk: a pooled analysis of over 4,300 individuals found that 5.8% had confirmed celiac disease, representing a sixfold increase compared to the general population.
First-degree relatives of someone with celiac disease also carry elevated risk, estimated at 10 to 15%, because they’re more likely to share the same HLA gene variants. Having an autoimmune thyroid condition or Turner syndrome also increases susceptibility.
Changes in the Modern Food Supply
The rising incidence of celiac disease over recent decades has prompted questions about whether changes in how food is made play a role. One line of research points to microbial transglutaminase, a bacterial enzyme widely used in industrial food processing to improve the texture and shelf life of baked goods, dairy, and meat products. This enzyme does something remarkably similar to the human enzyme involved in celiac disease: it modifies gluten peptides in ways that make them more resistant to digestion and more likely to be flagged as foreign by DQ2 and DQ8 immune receptors.
There is a direct positive correlation between the rising use of industrial enzymes in bakery products and the rising incidence of celiac disease over the last four decades. Testing blood samples from celiac patients, researchers found that more antibodies were active against complexes of transglutaminase bound to gluten fragments than against either component alone, and this antibody count was the best predictor of intestinal damage. The industrial enzyme may also directly weaken the intestinal barrier by modifying the proteins that hold gut cells together, compounding the zonulin-driven permeability problem.
Gut Bacteria and Early Life Factors
The composition of bacteria in the gut appears to differ in people with celiac disease, with a pattern of increased harmful bacteria and decreased beneficial bacteria. Whether this imbalance contributes to causing the disease or results from it remains an active question, but several early-life factors that shape the microbiome, including cesarean delivery, antibiotic exposure, and infant feeding practices, have been linked to celiac risk.
The timing of gluten introduction in infancy has received particular attention. A clinical trial found that introducing small amounts of gluten starting at 4 months of age, alongside breast milk or formula, resulted in zero celiac diagnoses among 488 children by age 3, compared to 1.4% of children who followed the standard introduction timeline around 6 months. The recommended early dose was about 4 grams of wheat protein per week, roughly equivalent to two small cereal biscuits. However, researchers caution that it’s not yet clear whether early introduction truly prevents celiac disease or simply delays its onset.
Why It All Comes Together Differently for Each Person
Celiac disease doesn’t have a single cause. It requires the genetic predisposition, exposure to gluten, and one or more environmental triggers that break immune tolerance. For one person, the trigger might be a childhood viral infection. For another, it might be a course of antibiotics that shifts gut permeability at a critical moment. The industrial processing of modern wheat products may add an additional layer of risk that didn’t exist a few generations ago. This is why celiac disease can appear at any age: someone can carry the genes and eat gluten for decades before an infection, pregnancy, surgery, or period of severe stress provides the final push that activates the disease.