Acid and Lignin Free
Acid is naturally found in paper, and over time it breaks down the fibre of the paper, causing it to become dry and brittle, eventually deteriorating into dust. The fact is that acid always migrates from an acidic material to a less acidic or neutral one. Protecting your photos begins with shielding them from acid naturally occurring in air, water or on your hands, as well as using acid free paper and plastic to store and display them in.
Paper made to the international standard ISO9706 is considered archival and permanent, and therefore called acid free.
Lignin is a substance found naturally occurring in the cells of plants -- including trees. Lignin in paper can react with light and heat to make the paper acidic, causing it to yellow and deteriorate. Again, ISO 9706 paper is lignin free.
Usually items designed for scrapbooking will state that they are acid and lignin free - but check before you buy, or ask if you are not sure - all crafters know how important this is and so won't mind you asking!
Other things to watch out for:
Heat - too hot or too cold can cause your photos to degrade - avoid storing your scrapbooks in an attic or garage or near a radiator.
Light - can fade your pages - always store scrapbooks closed and away from sunlight.
Your Hands - yes your hands - it is hard to avoid when making up your scrapbook pages, but obviously make sure your hands are clean and dry. Once made though, make sure your pages are keep inside page protectors.
Plastic - PVC contains chemicals which can age and yellow your photos - so avoid and use an alternative plastic.
Polyester: polyethylene terephthalate commonly known by names like Mylar, is transparent, strong and chemically stable and safe for your photos.