The most common result of improper film handling and storage is fogging of the film. Fogging is an obscuring opacity (darkening) on an x-ray film caused by many things. Film is packaged in polyethylene (black plastic) or metal foil (white paper with foil on the inside) to prevent fogging.
Excessive temperature and humidity can cause film fogging. Film should be stored in temperatures less than 70ºF and a humidity level around 50%. An unopened package of film is protected from humidity; however, it is not protected from the effects of high temperature. High humidity encourages fog and low humidity encourages static.
Before opening a box of film, be aware of its expiration date. Only use film that is not past its expiration date to avoid fog caused by age. Rotate the film stock using the First-in First-out (FIFO) method. The FIFO method is the idea that the first box of film (with the oldest expiration date) placed on the storage shelf is the first box used.
The position that film boxes are stored is important. Boxes should be stored upright, not stacked on top of each other. Pressure marks, as a result of stacking film boxes, results in a loss of contrast. Larger film boxes are more susceptible to this problem. Films can also be fogged by scatter from x-ray rooms and radionuclides from nuclear medicine; therefore, do not store unopened boxes of film near a radiation source. Unintentional exposure may occur if stored film is not protected from radiation.