But not all eye discharge is harmless. If you notice a big increase in the amount, or if it’s paired with redness, itching, pain, or blurry vision, it could be a sign of infection. Conditions like conjunctivitis (pink eye) can cause symptoms like these, and it’s important to see a doctor if they appear.

So the next time you wake up with a little crust in your eyes, don’t be alarmed—it’s usually just your body doing its job. That tiny bit of gunk is actually a small reminder that your immune system is always on duty, even when you’re fast asleep.