Degradation of emulsions presents similarities and differences to that of oils. Emulsions are metastable states, and therefore will suffer irreversible damage when heated or cooled below the temperature domain within which they maintain their metastability. This is an instance of degradation attributable to a physical cause.

Chemical and biochemical degradataion of emulsions has been dealt with in various sections already.

Chemical degradation by hydrolysis at the interface is not very important, because this uncatalysed reaction is extremely slow. On the other hand, surface active agents will in principle be occupying this interface, and might even provide physical barriers to species which would react with components of the inner phase. Chemical oxidation of emulsions can be a very taxing phenomenon indeed, and those whose inner phase is hydrophobic (i.e. o/w) are especially prone to it. The water phase acts as a good carrier of oxidising species to the interface, and therefore it is immediately at this interface that oxidation will occur. The surface active agents present at the interface may help delay oxidation by lessening the rythm of mass transfer of oxidants, but may provide reactive centers at a later stage of this phenomenon. Thus, carbonyl compounds formed from peroxidised fatty acids will easily react with amino compounds from protein present at the globular interface as a surface active ingredient. The resulting chemically altered protein may loose some of its surface active properties and its isoelectric pH will change. As more and more of its amino groups are used in such a fashion, the protein will complete chemical denaturation.

Biochemical degradation by the action of lipase enzymes is especially important and occurs at the interface as mentioned. Other surface phenomena which will occur include oxidation mediated by oxidising enzymes also mentioned earlier.

Protection against oxidation may be provided by antioxidants as well as by a series of good manufacturing practices. These will be dealt with below, but an important phenomenon, termed "the polar paradox", will be mentioned straight away. This refers to the fact that against what would intuitively be thought, the most effective antioxidants in dispersions are those whose solubility is higher in the dispersed phase, hence tocopherols over ascorbate in o/w emulsions and ascorbate over tocopherols in the w/o systems.