Slides unfortunately are quite sensitive. When exposed to moisture, light or heat the dye colors in the slide can start to fade. It can make the colors shift to a red or blue hue which can be corrected to a point but some slides become too damaged for accurate recovery. There can be other problems too such as the film can get easily scratched or even have fungus growth if moisture has been left on the surface. Keeping them locked away in a dark and dry environment will keep them preserved but all slides will deteriorate which is why it’s a great idea to make them digital.