The chemical risk to food from a food contact material arises from the transfer (= migration) of constituents from the material to the food. In practice, there is always some migration of substances when the material comes into contact with food. The harmfulness and quantity of the migrating substances are essential in assessing the risk.
The transfer of chemicals from contact materials is influenced by factors such as.

• The concentration of the migrating substance in the material - the higher the concentration, the greater the amount that can migrate.
• The molecular weight of the migrating substance - a small molecular size facilitates migration.
• The thickness of the contact material and the tightness of the material can slow down/prevent migration (interface thickness refers to the thickness of the contact material beyond which migration no longer increases but levels off).
• Food properties, such as greasiness and acidity, increase migration.
• Food temperature - migration increases several times for every 20 C increase in temperature.
• Long contact time with the food allows for greater migration. Migration is proportional to the square root of time - it increases rapidly at the beginning of the contact period, but levels off towards the end.
• Chemical similarity between the migrating material and the food - like dissolves like, e.g. a polar substance migrates more easily into a polar food.
• Large contact surface area relative to the volume of the container/container causes the greatest migration.

The mechanisms of migration are dependent on, among other things, the type of material. In a contact material composed of several different types of materials, migration can occur in several ways, e.g. by diffusion, dissolution, adhesion or set-off phenomenon.