Hooded eyes occur when the skin of the upper eyelid folds over onto the crease, creating a shadow that partially or fully obscures the mobile eyelid. This can be due to a prominent brow bone, excess skin, or a combination of factors. Hooded eyes can be classified as monolid (no visible crease), partially hooded (a crease is visible but the hood partially covers it), or deeply hooded (the hood fully covers the crease).