Issues with photos fading started with photograpy itself.  Concerns date back at least as far as the Photographic Society of London's "Fading Committee" of 1855. 

But the photos we are all most concerned about aren't quite that old! They date from 1936, with the introduction of Kodachrome film for 35mm slides, to about 1990, and it's these photos that are particularly in danger. 

Varying forms of a chromogenic process was used to print these photos. That simply means that the surface on which the print is made does not already contain the dyes necessary to make the colors required. So that, the process relied on checmical reactions to develop the dyes while the processing was happening. And it is the combination of dyes — typically, cyan (blue), magenta (red), and yellow — that creates the final colors we see in a color photo.

  

Fading is reality:

The sad truth is that these dyes (created by those chemical reactions) are not durable. As a matter of fact, they began to shift as soon as the photo was developed! And light hitting a photo — nearly any kind of visible light — simply accelerates this process. Now you know why film packages have disclaimers on them telling you that the colors may fade.

Typically, there are two effects:

1. a loss of detail in general, particularly in the highlights.
2. color shifts. The photo will change to appear to have a slightly green-like look. This is due to the magenta dye changing first, it is much more sensitive than the others.

Over the last 50 years, there have been many different chromogenic approaches to making prints. As the work of image permanence pioneer Henry Wilhelm has shown, these approaches do vary widely in terms of potential image permanence. Unfortunately, the most popular of these — for example, Ektacolor-processed prints from the 1960's and 1970's — have tended to have significant fading problems when exposed to light. 

If your photos are already faded:

Prior to the availability of a photo scanning service and digital photography software, if your photos were faded you were largely out of luck. That's not true any more!

Once an image is scanned it can be digitally manipulated to reduce that faded look. However, if your photos are severely faded, it can be challenging to bring them back to life — so it's definitely in your interest to hurry.

These are some other issues that have to be confronted when reviewing photos;

Color shift:

…fading that happens while stored. All photos, negative strips and slides degrade even without light. There are ways to slow the process.

Scratches:

…the invisible enemy. All of these forms of photograhic imagery are easily scratched and very susceptible to abrasion. There are things you can do to avoid them.

Disasters at home:

…why your photos aren't that safe at home. Aside from the obvious deterioration that we have already discussed, there are "home-bound" disasters that can, and do happen. Sometimes the disaster is called “pets” or “kids”, these (and others) are nonetheless a genuine threat. But our research shows that some kinds of disasters are lot more likely than others.

Wanna Do it yourself?

Some things to consider…If you want to scan and repair your own photos, you're a brave person, since it's not easy and a really big commitment.  However, we do have some advice for those hardy souls.