Relative humidity is the single most important factor in preserving photographs from chemical deterioration. Damage caused by fungi and other microorganisms is irreversible. Temperature control is improtant mostly because of its influence on relative humidity. However, high temperatures will speed up chemical deterioration. Fahrenheit is the recommended compromise temperature for the storage of photographs and the comfort of people, but lower temperatures are desirable, expecially for color materials.
Stable conditions are very important.
Photographic materials are hygroscopic, readily absorbing and releasing moisture. They expand and contract with fluctuations in environmental conditions and these dimensional changes accelerate deterioration. Particulate matter and harmful chemicals in the air can damage photographs. Ideally air should be filtered for these materials, and dust should be kept to a minimum. Light can cause embrittlement, yellowing, and fading in photographs.