Gluten is a protein found in wheat, rye, and barley. Some people experience unpleasant symptoms after eating it — but not always for the same reason. Celiac disease is an autoimmune condition. When someone with celiac disease eats gluten, their immune system damages the small intestine's lining, preventing nutrient absorption.  Symptoms include bloating, diarrhea, fatigue, joint pain, brain fog, and skin rashes. Long-term, it can cause malnutrition, osteoporosis, and other serious complications if untreated. Gluten intolerance, or non-coeliac gluten sensitivity, causes similar symptoms — like bloating, fatigue, or stomach pain — but doesn't damage the intestine or trigger immune responses. When seeking a diagnosis, doctors first rule out celiac disease and wheat allergy. Then, a dietitian may supervise a gluten-free trial to see if symptoms improve. Some people avoid gluten without a diagnosis, but this can lead to nutrient deficiencies if not managed properly.  Celiac disease is much more severe. Even 50mg of gluten, which is about 1/100th of a slice of bread, can cause harm. People with gluten intolerance might feel unwell from consuming small amounts of it, but they don't experience intestinal damage, like those with celiac disease.  For proper testing and advice, speak with a doctor or accredited dietitian. Self-diagnosing can do more harm than good.