Bad storage conditions are the main reason for damage to and deterioration of collections of photographic material. Factors influencing the state of conservation of photographic materials include temperature, relative humidity (RH), light, and chemicals (e. g., the materials themselves, developing and fixing compounds, chemicals from air pollution, or packing materials). Humidity could be the most important factor in the decay of photographs. The temperature greatly influences the RH. Changes in temperature also cause shrinkage and expansion and lead to mechanical damage. Light helps in breaking down organic substances such as emulsion, dyestuffs, paper, and carriers derived from cellulose. Air pollution chemicals may oxidize or otherwise transform the image silver; celluloid produces its own nitrogen oxides, formic and acetic acid from wood products affect the image layer photographic chemicals can cause destruction from inside, regardless of storage conditions. The most general advice is to keep photographs dark, cool, dry, and clean in a proper envelope. Take care of the inventory. More specific conditions depend on the materials and are given in ANSI standards. Some examples are given. On the average 15-20°C and 40-50% RH provide a good starting point.