Natural (and not-so-natural) Enemies of Photographs
The physical enemies of photographs include obvious villains (like direct sunlight, insects and rodents) and those that are more subtle: adhesives that degrade over time, sulfur compounds that can be given off by wood or rubber and trigger fading, and high humidity that can encourage mold growth. Experts advise against storing photographs in basements, attics and garages. They recommend storage materials specifically designed for long-term stability (called “archival” products). Surprisingly, many of the products sold by frame shops and retailers contain materials like high-acid wood pulp and Polyvinyl Chloride that can trigger deterioration. So the first set of recommendations is based on common sense: use archival materials and keep your photographs away from bright light, widely fluctuating humidity, and extreme temperatures.
From the American Museum of Photography