Naphthalene syndrome is an early indication of decomposition of early cellulose diacetate films. An odour of naphthalene, reminiscent of mothballs, that may surround these early cellulose diacetate films.
Early cellulose diacetate films used monochloronaphthalene as a plasticiser. As the film base decomposes the acid levels in the film base increases. This makes an environment unsuitable for the plasticisers to remain performing their function and the plasticiser molecules tend to migrate to the surface of the film.
Naphthalene’s low threshold of smell makes it very noticeable at low concentrations.
Manufacturers eventually changed the plasticiser to triphenyl phosphate (TPP) which does not have such a characteristic smell.