An autoimmune disease is a condition where your body's defense system attacks itself by mistake. Your immune system normally protects you by fighting off germs, viruses, and infections. It's like having security guards that keep harmful invaders out. But in autoimmune diseases, those guards get confused and start attacking your own healthy cells, as if they were the enemy.

Type 1 diabetes is an autoimmune disease where the immune system destroys cells in the pancreas that make insulin. In rheumatoid arthritis, it attacks the joints, causing pain and swelling. In celiac disease, eating gluten triggers the immune system to damage the small intestine.

Scientists don't fully understand why some people develop autoimmune diseases. These conditions can't usually be cured, but doctors can often help manage symptoms with medicine that calms down an overactive immune system. Some autoimmune diseases are mild and barely noticeable, while others require careful, ongoing treatment.

When someone says they have an autoimmune condition, they're explaining that their body needs extra help keeping its defense system in balance.