Many types of squid have the ability to alter the color of skin cells called chromatophores, in order to blend in with their environment. This allows them to hide from predators, and is often triggered when the squid feels threatened. These same squids, including the Humboldt squid (Dosidicus gigas), are commercially fished in parts of North and South America.

Now, researchers working in Spain and Mexico have identified the pigments in Humboldt squid chromatophores as ommochromes. Chemical analysis showed that the main violet-coloured ommochrome is a compound called xanthommatin, which the researchers found to have strong anti-microbial properties. Their study showed that xanthommatin could inhibit the growth of several microorganisms that can cause disease in humans, including the fungus Candida albicans (which causes thrush and yeast infections) and bacteria like Salmonella enterica. 

Skin from the squid is often discarded as waste from fisheries, but this new research tells us that it could be used to produce valuable medical compounds. The dumping of squid skin as waste "generates pollution problems in the coasts," says study co-author Jesús Enrique Chan in a news release, "so research like this, in which we inform about how these wastes could be used, helps to revalue them."  

Humboldt squid aren't the only squid that produces this pigment. The tiny Hawaiian bobtail squid (Euprymna scolopes) also produces the anti-microbial xanthommatin pigment, as do many other species.