What if your body’s greatest defender turned into your worst enemy? That’s the nightmare of autoimmune diseases, where your immune system mistakes you for the threat. In this video from Kurzgesagt, we learn how conditions like Type 1 diabetes, multiple sclerosis, lupus, and Crohn’s disease aren’t caused by invaders but by your own cells going rogue.

Your immune system is a terrifyingly efficient army of cells trained to kill anything unfamiliar. But sometimes, through genetic risk and a dose of bad luck, that army gets the wrong orders. One mistaken identity, one unlucky cold, and boom, your body launches a full-scale assault on your nerves, joints, pancreas, or anything else in range.

This explainer breaks it all down with vivid analogies (think baristas under sniper fire) and clear science. Check it out!