Microorganisms need organic materials to supply nutrients and, therefore, museum objects composed of organic materials are potentially at risk. Cellulose-based materials, such as cotton, linen, paper and wood, and proteinaceous materials such as leather and hair loth are particularly susceptible to direct attack by microorganisms.

Inhospitable materials, such as plastics, are not immune from fungal growths but how they support these growths is not fully understood by biologists. Certain mites feed on fungi and can carry spores onto normally resistant materials. As the mites die, they become the nutrients for a new fungal colony. This ability to exist on almost any material characterizes microorganisms as primary agents of deterioration.