Micro Ondes

Microwave ovens and chemicals in food packaging

Reheating at high power settings increases the risk of substances migrating into foods

The food industry currently offers a wide range of food products designed for quick reheating in the microwave oven. In partnership with the French National Consumers Institute (INC), ANSES has conducted a study on the risks of chemical substances migrating from packaging into foods during heating. The findings have prompted ANSES to recommend that consumers carefully follow the preparation instructions on the packaging of microwaveable food products.

Misuse of microwave ovens may pose risks

Microwave ovens are often used to save time when preparing meals. Manufacturers are aware of new food consumption behaviours and patterns and now offer well-suited products. Meals can now be ready to eat in less than 5 minutes.

Manufacturers are legally responsible for the safety of the preparation methods used. They are in charge of providing instructions on their product packaging that must be followed to ensure safe and appropriate use.

However, the impact of heating practices on consumer exposure to the substances found in packaging materials has not been widely studied and few data are currently available.

A subject currently under examination

ANSES has conducted work on this topic in partnership with the French National Consumers Institute (INC). Studies have been made on different types of packaging, including food bags for use in conventional and in microwave ovens, bags for steam cooking and microwave ovens, and ovenable food trays.

In the samples taken, polypropylene is the most commonly used polymer, regardless of the type of food packaged. For ovenable food trays that can be heated in both conventional and microwave ovens, tests conducted under three types of heating conditions (ambient temperature, heating in a microwave following the manufacturer's recommendations, and “extreme” heating) revealed the presence of POSH  (substances potentially used as lubricants) in several samples kept at ambient temperature. POSH levels increased during reheating, especially in cases of extreme heating (high temperatures and long heating times).

At excessively high power levels, microwave heating increased the risk that the substances present in the packaging would migrate into the food.

ANSES recommendations

The results of this study have led the Agency to advise customers to follow the manufacturers' recommendations (power level and cooking time) indicated on the food packaging, since extreme reheating increases the risk of substance migration.

The Agency also recommends avoiding damaged or used packaging for reheating.  
It also strongly discourages the storage or reheating of acid-based foods (tomatoes, recipes containing lemon juice, etc.) in aluminium foil, since acidity increases migration of the aluminium into food.  

A few reminders about packaging and reheating methods

For optimal use of your microwave oven, ANSES issues the following recommendations:

  • always check that the recipient used for reheating is compatible with microwave oven use (this should be indicated by the manufacturer) and that it is in good condition;
  • do not keep single-use packaging for reuse as a container for microwaving food (e.g. do not reuse food trays);
  • prefer longer reheating times at lower power settings (e.g. 2 minutes at 650W is preferable to 50 seconds à 1270W), especially if no specific instructions can be found on a food's packaging;
  • avoid the use of microwave ovens for heating infants' feeding bottles: the uneven temperature distribution within the formula could potentially burn the child.