The exact composition of Xenomorph blood is a vigorously debated topic. Its extreme corrosiveness precludes study to a large degree. However, it is known that it is some form of molecular acid, and that while incredibly potent, it quickly oxidizes in air and is subsequently rendered neutral. It is typically a dull yellow in color, occasionally with hints of green. While generally accepted as the creature's blood (and typically described as such), some have suggested that, at least at the Facehugger stage, the acid is not blood but rather a defensive fluid maintained under pressure between a double layer of skin.