Are you wondering if it’s safe to use your stainless steel cookware? Searching the internet for answers can be confusing because some tout it as among the safest of choices and others deem it a toxic source of heavy metals and recommend complete avoidance. A more detailed assessment reveals that the safety of stainless steel is more complicated than a “use it” or “avoid it” label. Some individuals can use it safely under certain conditions while others should avoid it completely. Let’s break it down.
What Are the Concerns About Cooking with Stainless Steel?
Studies show that stainless steel cookware can leach nickel and chromium into acidic food. Before we get into specific results of these studies, let’s look at the health effects of nickel and chromium.
Is Nickel Harmful?
Nickel is an essential micronutrient that plays an important role in human metabolism (1). Too much nickel can be toxic, and therefore the National Academy of Sciences sets a Tolerable Upper Intake Level (UL) at 1000 µg (micrograms) per day. Adults ingest an average of 69-162 µg per day. Most nickel exposure comes from food and water. Foods that are naturally high in nickel include chocolate, soybeans, nuts and oatmeal. Once nickel is ingested it is removed by the kidneys and quickly passed out of the body.
Jewelry that contains nickel can also be a significant source of exposure and is thought to be why women are more at risk of developing nickel sensitivities than men. An estimated 10-20% of the population have a sensitivity to nickel that leads to dermatitis. For those who are sensitive, a single dose of 67 µg can cause a flare up or lead to systemic dermatitis.
The most serious risk is to people who breathe dust containing nickel compounds while working in an industrial setting. The EPA has determined that, under these conditions, nickel is a carcinogen.
Is Chromium Harmful?
Chromium is not as much of a health concern as nickel. It is an essential trace mineral in the human diet but is poorly absorbed. The recommended intake for adults is 50-200 µg and the most adults get 60-80 µg from their diet. Up to 7% of the population may have a chromium sensitivity that can cause dermatitis (2).
How Much Nickel and Chromium Leach During Cooking?
One study found that nickel and chromium leached into acidic food. A number of variables were studied:
The grade and composition of the stainless steel. The most common grades of steel are 304 and 316. The grade refers to the quality, durability, and heat resistance. Higher numbers mean higher quality. Many cookware items will also have a ratio, such as 18/8 or 18/10, which tells the percentage of chromium and nickel, respectively. This study did not find a correlation between the percentage of nickel and the amount of nickel leached, so it is unclear if there is any advantage to buying 18/8 over 18/10. Similarly, the study did not show that the higher grade (316) leached less than the lower (304) in all cases.
The cooking duration. In general, the longer cook times resulted in more leaching.
The age of the cookware. New cookware leached significantly more nickel and chromium. After the 6thcooking cycle, the amount of leaching levelled off.
On average, after the 6thcooking cycle, the cookware leached 88 µg of nickel and 86 µg of chromium. This is well within the Tolerable Upper Intake Level of 1000 µg. For perspective, a ½ cup of peanuts contains 68 µg of nickel. So, cooking with stainless steel may add a significant amount of nickel to an average daily intake but still be within acceptable levels. All tests were done using a high-acidic food (tomato sauce), so presumably foods with lower acidity would result in less leaching. It is important to note, however, that sensitive individuals could react to just one meal cooked in stainless steel cookware.
Recommendations for Using Stainless Steel Cookware.
- If you have a known sensitivity to nickel or suspect you may have one, avoid all stainless steel cookware.
- If your cookware is new, wash it thoroughly. Cook a solution of 50% vinegar and 50% water for a 2 hour period and discard the solution. Repeat these steps 6 times (3).
- There is a very high grade of stainless steel (430) that has only trace amounts of nickel. If you can afford it, look for cookware with this grade. Avoid any products that have an aluminum core as it could leach aluminum if deeply scratched.
- Avoid cooking highly acidic food, such as tomato sauce or chili, for long cooking durations.
- Rotate your cookware so that you do not get too much exposure to the same materials.
If you are simply more comfortable avoiding stainless steel cookware, it is a personal choice and do what it right for you. But, if you hate the idea of giving up your favorite pot or pan, follow these simple guidelines and keep cooking.