thumb|Shrinking and warpage of [[16 mm film caused by vinegar syndrome]]

thumb|Bubbling and warpage of a laptop's [[Liquid-crystal display|LCD polarizer caused by vinegar syndrome]]

Vinegar syndrome, also known as acetic acid syndrome, is a condition created by the deacetylation of cellulose acetates (usually cellulose diacetate) and cellulose triacetate. This deacetylation produces acetic acid, giving off a vinegar odor that gives the condition its name; as well, objects undergoing vinegar syndrome often shrink, embrittle, and form crystals on their surface due to the migration of plasticizers. Vinegar syndrome widely affects cellulose acetate film as used in photography.

The film preservationist Harold Brown is credited with coining the phrase "vinegar syndrome".

The progression of degradation

thumb|Still photograph exhibiting damage due to vinegar syndrome

In acetate film, acetyl (CH<sub>3</sub>CO) groups are attached to long molecular chains of cellulose. With exposure to moisture, heat, or acids, these acetyl groups break from their molecular bonds and acetic acid is released. While the acid is initially released inside the plastic, it gradually diffuses to the surface, causing a characteristic vinegary smell.

The decay process follows this pattern:

  • Acetic acid is released during the initial acetate base deterioration, leading to the characteristic vinegar odor. This signal marks the progression of deterioration.
  • The plastic film base becomes brittle. This occurs in the advanced stages of deterioration, weakening the film and causing it to shatter with the slightest tension. These physical changes happen because cellulose acetate consists of long chains of repeating units, or polymers. When the acetic acid is released as these groups break off, the acidic environment helps to break the links between units, shortening the polymer chains and leading to brittleness.
  • In some cases, pink or blue colors appear in some sheet films. This is caused by antihalation dyes, which are normally colorless and incorporated into the gelatin layer. When acetic acid is formed during deterioration, the acidic environment causes the dyes to return to their original pink or blue color. These tools can be used to determine the extent of damage to a film collection and which steps should be taken to prolong their usability.