Why have pictures from the late 70s turned red?

Why have pictures from the late 70s turned red? This isn’t how they looked when they came to us fresh from the printer. What’s happened?

What you’re seeing is the fading or loss of the green and blue sensitive parts of the photo paper. We may not always know what brand of photo paper was used for any given print (some have the company’s name on the back, some don’t), but apparently there was a popular culprit.

Agfacolor Paper Type 4 was in production from 1974-1982 and was popular among portrait studios. Apparently many photographers using this paper knew it had a short life span, but they felt the accuracy of color, especially skin-tones, at the time of production made it worth it. Processing included a formaldehyde soak at the end to try and lock in the color and prevent fading for as long as possible.

But it obviously didn’t work. This is a picture of me that has been red for as long as I can remember, so, probably about 4-5 years after it was taken.