They're pungent to the eyes and other organs because of the presence of Capsaicin, the colourless and odourless substance which is concentrated in pepper.

This substance induces a burning sensation in your eyes, tongue or just about any part of the human body that it comes in contact with. If you happen to eat a lot of pepper and your mouth feels like it's on fire, don't drink any water, it'll only spread the Capsaicin over your tongue. Your best bet is to take some yoghurt or milk which will help dissolve it and provide some fast relief.