Since this article deals strictly with conservation, restoration generally being shunned by philatelists, it concentrates on the 4 broad categories of damage: 1) physical, caused by improper handling such as careless removal of paper fragments from the back of stamps or exposure of light-sensitive material to light sources; 2) atmospheric, unused postage stamps containing materials making them especially vulnerable to unsuitable conditions of temperature and humidity; 3) chemical, not only confined to atmospheric pollutants; and 4) biological, exemplified by molds being attracted to gelatin-sized paper as a food source. The greatest difficulty is that damage, generally, cannot be traced to a single source but to a combination of factors relating to the various materials that make up a stamp. The most recent PVA and PVOH adhesives have shown greater resistance to damage in laboratory experiments but only the passage of time will confirm their durability under actual atmospheric conditions.