Aspergillus niger black mould fungi, illustration. Aspergillus niger is the causative agent of black mould on the outside of spoiled foods. This is a toxic fungus that causes diseases in humans. These include fungal ear, lung and skin infections (otomycosis, pulmonary aspergillosis and mycotic keratitis). It also produces aflatoxin, one of the most powerful naturally occurring carcinogens. This can cause cancers and disorders of the lung, liver, spleen, stomach, colon and kidney. Similar fungal morphology is present in Aspergillus versicolor and some other Aspergillus fungi.