Fungi are simple-celled organisms that do not need energy from light for growth. The fungi bear microscopic spores that are produced in enormous quantities, are always present in the air, and spread via air currents. They are often water repellant and are resistant to desiccation (drying out). Extreme cold and heat will destroy them.

When the spores are in favorable environment, they will germinate. What constitutes a favorable environment is different for each species. After landing on a host material, a spore must obtain sufficient moisture to germinate and find enough food. Without moisture, the spores will lie dormant until favorable conditions occur.

For this reason, it is important to control the environmental conditions where museum collections are stored or exhibited. The NPS "Museum Handbook," Part I (Rev 9/90), Chapter 4, recommends that temperatures not exceed 24 degrees C (75 degrees F) and relative humidity (RH) not rise above 65%. These conditions are maximum levels and only reduce the potential for microorganism growth. They do not eliminate he threat. Some microorganisms can grow in significantly lower temperatures and at lower RH levels. Certain materials need to be stored with lower RH levels to prevent growths. Refer to the NPS "Museum Handbook," Part I (Rev 9/90), Figure 4.3, chart for the RH target levels for various materials and types of objects that are housed in park museum collections.

NOTE: Some species of microorganisms cause health risks in the form of chronic lung irritation. Always exercise caution when handling badly infested materials, i.e. wear a high-efficiency particulate air (HEPA) filter respirator and disposable gloves. (See also "Conserve O Gram" 16/1).