Many people wrap hot, acidic food in aluminum foil, but a study found that cooking with foil leaches aluminum into the meal, especially with tomatoes, vinegar, and spices

Aluminum foil is a kitchen staple nobody thinks twice about, whether you're sealing up a foil packet of chicken and veggies or lining a baking sheet before it goes in the oven. It's cheap, it's convenient, and it feels completely harmless. But that shiny piece of metal may not be as inert as it appears.

According to a 2012 study published in the International Journal of Electrochemical Science, foil can quietly shed aluminum into whatever it touches. If your go-to dinner involves a tomato-based marinade, a splash of vinegar, or a heavy hand with the spice jar, this one is worth a read.

What the researchers actually did
According to the same study, ‘Risk Assessment of Using Aluminum Foil in Food Preparation,’ a team of chemical engineers in the UAE and Egypt tested how much aluminum leaches out of foil during everyday cooking. They made several meat sauces with varying combinations of tomato juice, citric acid, salt, apple vinegar, and spices, and exposed foil strips to the boiling liquid, its steam, and food cooking under foil in an oven.


They then measured the foil to see if any metal had been lost, studied its surface with a scanning electron microscope, and used mass spectrometry to determine how much aluminum had been transferred to the food. This is a small, lab-based study and not a clinical trial, but these are standard, credible methods to track metal leaching.

The findings that should make you pause
In every test, some weight was lost from the foil, which meant metal was leaching into the food. Depending on the amount of foil covering the pan, a family-style meal prepared with a mild tomato and citric acid sauce added 22.8 to 75.4 milligrams of aluminum per person, the study found. Increasing the citric acid level brought that up to the 40 to 132.4 milligram range.

The type of water also played a role. The same recipe made with tap water leached about half the amount of aluminum, some 65.2 milligrams per person, compared to the version made with drinking water, at 132.4 milligrams. Even just tomato juice made a difference. The study also found that adding tomato juice to plain meat extract, without acid or salt, more than doubled leaching by dropping the pH of the solution from 6.9 to 4.9.

Vinegar and spices were the biggest wild cards
Swapping citric acid for apple vinegar changed things dramatically. According to the study, a sauce made with apple vinegar leached about 465 milligrams of aluminum per person, more than three times the amount leached from the citric acid sauce. Spices were more dramatic. Researchers said that adding only 3 grams of spice to the same citric acid and tomato sauce made leaching about four times higher, at roughly 537.2 milligrams per person in one meal. They were unable to say exactly what compound was responsible but noted that organic acids and other complexing agents are known to more aggressively extract aluminum ions from the surface of the metal.

The oven made things worse, not better
The study reported that covering a roasting pan with foil and baking a similar sauce in a hot oven for ninety minutes produced combined leaching from both pan and foil of roughly 361 milligrams per person. Electron microscope images showed the foil surface was cracked, pitted, and, as the researchers put it, almost completely damaged. The higher the oven temperature, the faster this damage occurred, the researchers found. Heat thickens and restructures the thin oxide layer that normally protects aluminum from dissolving.

How much aluminum is actually too much
According to the WHO food safety experts at JECFA, as summarized by the European Food Information Council, adults can safely consume up to 2 milligrams of aluminum per kilogram of body weight per week. That’s about 136 milligrams a week for a 150-pound adult from all sources, food, water and cookware combined.

In this study, some of the foil-cooked meals, especially the vinegar and spice versions, have provided that much in a single meal. It’s a genuine health risk rather than a guaranteed harm, the study’s authors say, since the body excretes most dietary aluminum fairly efficiently, but regularly eating near or beyond that weekly ceiling is not something nutrition experts recommend.

This is not a one-off finding
A separate 2019 peer-reviewed study found that when researchers baked salmon, mackerel, duck breast, tomatoes, and other foods in foil, aluminum levels increased significantly after cooking, particularly in marinated dishes. Both studies find the same pattern: acid, salt, and heat make foil go from convenient to leaky.

What this means for your weeknight dinner
Nobody is asking you to throw out your foil. It is fine for wrapping sandwiches, storing leftovers, or lining a pan under something that won’t come in direct contact with acidic or heavily seasoned food. The concern is specific to tomato sauces, citrus or vinegar marinades, and spice-forward dishes cooked in direct contact with foil, especially at high oven temperatures or for long periods of time. Parchment paper, glass dishes, or stainless steel are easy swaps for those recipes. If foil-wrapped fish or chicken with a lemon and herb marinade is a weekly habit, this is a small kitchen adjustment worth making.