Many ingredients are derived from sources that are known to be allergenic. Very common examples would include peanut and soybean oils, soybean lecithin, and hydrolyzed milk, wheat, or soybean proteins. Less well known examples would include fish gelatin used to encapsulate certain vitamins and xanthan gum, a fermentation product made using wheat or soybean substrates.

When considering ingredients derived from an allergenic food source, the presence of the allergenic protein is an important consideration. Refined edible oils contain extremely low levels of residual proteins. Clinical trials have documented that refined peanut and soybean oils are safe for individuals allergic to the source food.

However, less highly refined oils including cold-pressed peanut oil and sesame seed oil can contain sufficient protein residues to elicit allergic reactions in individuals sensitive to the source foods. Lecithin can be derived from several sources, although soy lecithin is probably the most commonly used commercially.

Soy lecithin definitely contains residual amounts of soy protein and detectable soy allergens. Extensive surveys of the amount of protein in commercial soy lecithin have not been conducted although some variability is likely to exist because several different commercial processes are used.

Soy lecithin does not appear to elicit adverse reactions in the majority of soybean-allergic individuals, although clinical trials have not been conducted to critically examine the allergenicity of soy lecithin to such individuals. If the proteins have been extensively hydrolyzed, the allergenicity of the protein is likely to be eliminated.

For example, extensively hydrolyzed casein serves as the basis for hypoallergenic infant formulae recommended for milk-allergic infants. However, protein hydrolysates used in the food industry can vary widely in terms of degree of hydrolysis, and only those that are extensively hydrolyzed would be safe for individuals allergic to the source food.

Of course, hydrolysis of the protein can dramatically affect the ability to detect residual proteins, especially using immunochemical techniques, even in cases where residual allergenicity may remain. In other cases, the nature of the protein may have some impact on allergenicity.

Although fish gelatin is derived from fish, this ingredient is primarily composed of fish collagen while the fish allergens are primarily parvalbumins. Recently, fish gelatin derived from codfish skins was documented to be safe for the vast majority of codfish-allergic individuals at levels up to 3.61 g of cumulative intake.

If foods derived from allergenic sources contain detectable protein residues, the safety of these foods must be established by clinical trials in sensitive individuals. Alternatively, the foods should be labeled to declare the source of the ingredient.