The nature of these materials consists of at least two layers: the emulsion layer (particles and dyes) and the "support layer" (paper, plastic, etc.).
Temperature, humidity, light, pollution and contaminants can deteriorate them. You have to avoid the contact of photographic materials with these damaging factors.
The photos needs to be framed properly, stored in plastic envelopes and cleaned using a soft brush. You can also reproduce them and retouch them. It is a good idea to scan photographic prints and transfer film to dvd to provide a digital copy that can be stored away from the originals in case of fire, flood or other disaster.