Do microwaves, burnt toast or fried food cause cancer?

In a microwave oven, a part called a magnetron produces microwaves. These waves make the water molecules in food vibrate, and this vibration produces the heat that cooks the food ^[1].

• Microwave radiation is "non-ionising": it does not have enough energy to knock electrons out of atoms, and it does not carry the risks of X-rays ^[1]. Visible light and radio waves, such as those used by mobile phones, are of the same type ^[1]; see Do mobile phones cause cancer?
• Food does not become radioactive: when food absorbs microwave energy, it turns into heat and does not make the food "radioactive" or "contaminated" ^[1].
• Nutritional value: microwave cooking does not reduce the nutritional value of food any more than conventional cooking; because it cooks faster and without water, food may even keep more of its vitamins and minerals ^[1].

High levels of microwave radiation can heat body tissues the way they heat food and can cause skin burns or cataracts ^[1]. That is why microwave ovens are built not to let radiation out: the leakage limit in the United States is far below the level known to harm people, leakage falls quickly with distance from the oven, and the oven has two separate locks that stop the microwaves the moment the door is opened ^[1].

A microwave oven in good condition does not leak radiation; but if the door hinges, latches or seals are damaged, or the door does not open or close properly, contact the manufacturer ^[1].

Glass, paper, ceramic and plastic let microwaves pass through; but some plastic containers can melt from the heat of the food. The instructions that come with your microwave say which containers are suitable ^[1]. Metal pans and aluminium foil should generally not be put in a microwave either ^[1].

• Melamine dishes (lightweight, often colourful plastic tableware that looks like china): the US Food and Drug Administration advises not heating food or drinks in melamine dishes in the microwave, because at high temperatures, especially with acidic foods, more melamine moves into the food. Heat food in a ceramic dish or a container that is "microwave-safe", and then you can serve it on melamine ^[2].
• Plastic containers: do not use plastic that is not labelled "microwave-safe" to heat food or drinks ^[2].
• Microplastics: according to the US Food and Drug Administration, current evidence does not show that the amounts of microplastics found in foods pose a risk to human health, and there is not enough evidence that microplastics move from packaging into food; research is continuing ^[3].

Acrylamide is a substance that forms from natural sugars and an amino acid in plant foods such as potatoes, bread and grains when they are fried, toasted, roasted or baked at high temperatures. It does not usually form with boiling or steaming, and it is low in meat, dairy and fish ^[6]. Its largest sources in the diet are chips (French fries) and crisps (potato chips), coffee, breakfast cereals, biscuits and toast ^[6]. Very brown and burnt areas contain the most acrylamide ^[6].

• In animals: at very high doses, acrylamide has caused several types of cancer in rodents ^{[5, 6]}. In 1994 the International Agency for Research on Cancer, based on sufficient evidence in animals and inadequate evidence in humans, classed it as "probably carcinogenic to humans" ^[4].
• In people: in a review of 16 studies of more than a million people followed for about 15 years, those who ate more acrylamide did not develop more of any of the cancers studied; cancers of the female organs were not included in this review ^[7]. Another review that looked only at women's cancers found a small increase in ovarian and womb cancer with higher acrylamide intake, especially in women who did not smoke, and little link with breast cancer ^[8].
• The US National Cancer Institute's summary: many studies in people have found no consistent evidence that acrylamide in food raises the risk of any cancer; one reason is that it is hard to measure exactly how much acrylamide each person eats ^[5].

Cigarette smoke is a much bigger source of acrylamide than food: people who smoke have 3 to 5 times higher levels of acrylamide markers in their blood ^[5].

The main advice of the US Food and Drug Administration on acrylamide is a healthy, balanced diet; it does not recommend cutting down on whole grains and high-fibre foods to reduce acrylamide ^[6]. For coffee, see Does coffee or tea cause cancer?

In a large study in the United States, more than 100,000 women past the menopause were followed for nearly 20 years. Women who ate more fried food died slightly more often, and fried chicken and fried fish were linked to more deaths from heart disease; but fried food overall was not linked to death from cancer ^[9].

For fast food and factory-made ready meals, see Do fast food and ultra-processed foods cause cancer? and Does obesity cause cancer?

In a review of 16 studies of people who had never smoked (mostly women), several studies found that exposure to cooking oil fumes was linked to a higher risk of lung cancer ^[10]. In two studies, using an extractor fan was linked to a lower risk, and in other studies a kitchen without ventilation was linked to a higher risk ^[10].

A simple step: when frying or sautéing, turn on the extractor fan or open a window.

When meat, chicken or fish is cooked at very high temperatures or over an open flame, such as grilling over charcoal or pan-frying, chemicals form that damage DNA (the genetic material of cells) in the laboratory and have caused cancer in animals at doses thousands of times higher than in a normal diet ^[11]. Studies in people have not yet shown a definite link between these chemicals and cancer ^[11].

As a precaution ^[11]:

• do not put meat directly over the flame, and shorten the cooking time over very high heat; for example, part-cook meat in the microwave before grilling it.
• turn the meat often while cooking.
• cut off burnt and blackened parts, and do not use the meat drippings to make gravy.

For red meat itself and processed meats such as sausages and salami, see Does the cooking method matter?