Celiac disease is an autoimmune condition where eating gluten triggers your immune system to attack the lining of your small intestine. About 1% of the global population has it, though prevalence ranges from 0.7% to 2.9% depending on the region. The damage isn’t caused by gluten directly. It’s caused by your own immune cells responding to gluten as though it were a dangerous invader.
What Gluten Does Inside Your Gut
Gluten is a protein found in wheat, barley, and rye. When you eat it, your digestive system breaks it into smaller fragments called peptides. In most people, these peptides pass through without incident. In someone with celiac disease, those fragments set off a chain reaction.
The first key player is an enzyme your body naturally produces called tissue transglutaminase. This enzyme is released from cells during inflammation and chemically modifies gluten peptides in a process called deamidation. That modification is critical: it changes the shape of the gluten fragments just enough that they lock tightly onto specific immune system receptors on the surface of cells in the intestinal wall. Once locked in, these modified peptides are presented to immune cells as a threat.
The Immune Response That Causes Damage
The modified gluten fragments bind to specific molecules on your cells (called HLA-DQ2 or HLA-DQ8), which then activate a type of white blood cell called a T helper cell. These gluten-reactive T cells produce inflammatory signals, predominantly a powerful cytokine called interferon-gamma. Some also produce a second inflammatory signal called IL-17, amplifying the response. Interestingly, only about 0.5% to 1.8% of the immune cells in a celiac patient’s gut are actually reacting to gluten, but their inflammatory output is enough to cause serious tissue destruction.
At the same time, cells lining the intestine produce another inflammatory signal called interleukin-15, which activates a separate group of immune cells embedded in the intestinal lining. These cells, including an unusual subset called gamma/delta T cells, become persistently expanded in the gut and contribute to ongoing inflammation even beyond the gluten-specific response. The result is a two-pronged attack: one arm driven by gluten recognition, the other by broader inflammatory activation in the tissue itself.
How Your Intestine Gets Damaged
Your small intestine is lined with tiny, finger-like projections called villi. These dramatically increase the surface area available to absorb nutrients from food. In celiac disease, the sustained immune attack gradually flattens these villi, a process called villous atrophy. At the same time, the deeper tissue layers (called crypts) grow abnormally as the body tries to compensate.
Doctors grade this damage on a scale called the modified Marsh classification, ranging from Type 0 (normal intestine, celiac highly unlikely) to Type 3c (complete destruction of villi). Type 1 shows immune cell infiltration but intact villi, which can appear in people on a gluten-free diet who are still getting trace exposure. Type 3, the spectrum where symptomatic celiac disease lives, progresses from mild flattening to total loss of villi structure.
With fewer functioning villi, your intestine can’t absorb nutrients properly. This leads to the classic symptoms: diarrhea, fatty stools, weight loss, and failure to thrive in children. But the malabsorption also drives problems far beyond the gut.
Symptoms That Have Nothing to Do With Digestion
Many people with celiac disease present with symptoms that seem completely unrelated to their intestines, which is part of why the condition is frequently missed or misdiagnosed.
Anemia is the second most common way celiac disease shows up in adults, affecting roughly 15% at presentation. Poor calcium and vitamin D absorption leads to reduced bone density, with the body pulling calcium from bones to compensate. Joint inflammation is surprisingly common: in one study of 200 celiac patients, 26% had arthritis compared to just 7.5% of a control group.
The skin manifestation, dermatitis herpetiformis, produces intensely itchy blisters on the elbows, knees, buttocks, and lower back. Patients also commonly report dry skin, easy bruising, brittle nails, and thinning hair. Mouth ulcers and dental enamel defects are frequent oral signs.
Neurological effects are particularly striking. Gluten ataxia, which impairs coordination, balance, and gait, accounts for roughly half of the neurological presentations. About 39% of celiac patients in one study met criteria for peripheral neuropathy (numbness, tingling, or pain in the hands and feet) compared to 20.5% in healthy controls. In children, celiac disease can cause short stature and delayed puberty. Nearly half of patients have elevated liver enzymes at diagnosis, and up to 30% show reduced spleen function.
Why Only Some People Get Celiac Disease
Genetics plays a gatekeeping role. More than 90% of people with celiac disease carry the HLA-DQ2 gene variant, and most of the remainder carry HLA-DQ8. These genes code for the immune molecules that present gluten fragments to T cells. Without them, the key step in the immune cascade simply can’t happen.
But carrying these genes is not the same as having celiac disease. Between 30% and 40% of the general population carries HLA-DQ2 or HLA-DQ8, yet only about 3% of carriers ever develop the condition. Something else, likely a combination of environmental triggers, gut bacteria composition, infections, or other immune factors, tips genetically susceptible people into active disease. This is why celiac can develop at any age, sometimes after decades of eating gluten without problems.
How Celiac Disease Is Diagnosed
The first-line screening test measures antibodies against tissue transglutaminase (tTG-IgA) in your blood. This makes biological sense: since tissue transglutaminase is central to how gluten gets modified and presented to immune cells, the body produces antibodies against it as part of the autoimmune response. The tTG-IgA test has a sensitivity of 78% to 100% and specificity of 90% to 100%, making it highly reliable but not perfect.
A positive blood test is typically followed by an intestinal biopsy, where a small tissue sample is examined under a microscope and graded on the Marsh scale. This confirms whether villous damage is actually present. It’s important to keep eating gluten before both tests, because going gluten-free can normalize antibody levels and allow villi to heal, producing a false negative.
What Happens Without Treatment
Left untreated, celiac disease carries serious long-term consequences beyond malnutrition. The persistent inflammation and immune activation increase the risk of certain cancers, particularly a rare but aggressive form of intestinal lymphoma. Studies have estimated this risk at anywhere from 2.5-fold to over 100-fold compared to the general population, though more recent data suggests the risk is lower than older studies indicated and is concentrated mainly in older patients with prolonged undiagnosed disease.
How a Gluten-Free Diet Reverses the Process
Removing gluten stops the cascade at its source. Without gluten peptides entering the gut, there’s nothing for tissue transglutaminase to modify, nothing for HLA-DQ2/DQ8 molecules to present, and no trigger for the T cell response. The inflammation subsides, and the intestinal villi gradually regrow. Antibody levels in the blood drop, often returning to normal within months, though full intestinal healing can take a year or longer in adults.
The threshold for “gluten-free” in the United States is set at less than 20 parts per million, meaning a food labeled gluten-free must contain fewer than 20 milligrams of gluten per kilogram of product. For context, a single regular breadcrumb weighs roughly 500 milligrams, so the tolerance is extremely low. Even small, repeated exposures can sustain the immune response and prevent healing, which is why strict adherence matters more than occasional avoidance.