August 18, 2022 — Thursday
Why does stainless steel sometimes have a “Prop 65” warning?
Why do stainless cookware items have a “Prop 65” warning?
Isn’t stainless steel non-toxic?
Section #1) What is in stainless steel?
First, here’s a link to an article I wrote discussing this specific question. There are quite a few grades/alloys of stainless steel (for the hard-core curious types, here’s a chart listing a whole bunch of ’em — the most common ones used in high-quality cookware are 304, 316, & 400 Series). Plus, the composition of stainless steel actually varies across the decades. With the testing I have done and reported on this website, you can see many variations of stainless steel composition. Here are some examples:
- The 2022 Instant Pot Insert
- Solidteknics Noni Stainless Pans (my favorite pans, actually!)
- An Ikea Stainless Pan
- A Stainless Mug
- A Stainless Fork
- A Stainless Knife
Here’s a link to the category of articles on this website with a “Stainless Steel” tag. What most of these items have in common (as products made from the stainless composite metal that allows it to be called “stainless”) is that they contain some amount of Iron, Chromium, and Nickel. Other metals present in various Stainless Steel formulations may include Copper, Manganese, Vanadium, Cobalt, Bromine, and Molybdenum.
Section #2) Why do some stainless steel products have a Prop 65 warning?
Prop 65 is a labeling standard for California State. If a product contains a substance that California has determined may cause cancer or reproductive harm, the packaging and marketing information for that product (if/when it is sold in California) needs to include the appropriate Prop 65 language related to the toxicants/ chemicals/ metals contained in the product.
Per the statements below, from two different manufacturers of stainless steel products (see images at the bottom of this article), California considers Chromium and Nickel to be probable or known carcinogens. Most stainless steel has both Chromium and Nickel, as significant components, therefore requiring the Prop 65 warning as well. Some stainless steel alloys are either Nickel-free, or low-Nickel (400 series), and therefore considered safer/healthier for food-use products, based on these considerations. The most common stainless steel alloy found in kitchens today generally has about 170,000 to 180,000 ppm of Chromium and 78,000 to 82,000 ppm of Nickel. Manufacturers refer to this typical stainless steel alloy formulation — using 18% Chromium, and 8% Nickel, respectively — simply as “18/8”. This is also the typical makeup for items with the description “food-grade stainless,” or “medical-grade stainless.” The primary metal in stainless steel is Iron, of course — which is generally present at levels in the range of 700,000 to 800,000 ppm. Additional metals typically found in stainless steel (mentioned above), tend to be present at levels anywhere from 100 to 10,000 ppm.
Section #3) Isn’t Stainless Steel completely safe for cookware?
There have been some studies indicating that cooking in stainless products (or otherwise using stainless items for food-use purposes) may cause some of the metals contained in the stainless item to leach into the food contained in the item… I have carefully read several of those studies — and in my opinion, the cooking methodologies and tested usage of the item (as demonstrated in these studies) are not typical of the actual, anticipated uses for these items “when used as intended” by the manufacturer (and when used in the way most people typically cook their food).
Instead, the studies appear to have pushed the limit (as many studies do), not just to determine IF metals leach from stainless with cooking, but to see under what conditions/ what kind of usage might induce leaching (of Nickel or other metals) into the food cooked in a stainless pan (as an example). One of the most popular studies cited by cookware manufacturers attempting to disparage the use of stainless steel for everyday cookware (in promoting their non-stainless steel cookware) is a study in which tomato-based products (highly acidic) were cooked for a very long time (longer than one might typically ever cook tomatoes) to determine how much of the metals might leach into the tomato sauce under those conditions.
- Study Example — “Stainless Steel Leaches Nickel and Chromium into Foods During Cooking” (Published September 19, 2013):
- Most notable in this study — cook times used were from two to 20 hours (!) I personally don’t normally cook anything in a stainless pot or pan for more than 10 to 20 minutes — maybe (rarely) for an hour, at most. Also note the concluding sentence of the abstract (image below): “Stainless steel cookware can be an overlooked source of nickel and chromium, where the contribution is dependent on stainless steel grade, cooking time, and cookware usage.”
- Also notable in this study: the leaching decreases/ stabilizes over time (after the sixth use/cycle with “seasoning”). So if you wanted to rely solely on the information presented in this study, you could (in theory) buy some new stainless pans, put tomato sauce in the pan, cook for 20 hours (wash, rinse, and repeat six times) — and then any leaching for long-form cooking in these pans should be (at least) stabilized/minimized. Said another way: if you have been using your stainless pots for years (or decades), it is not likely there is an ongoing concern (with the exception being for those who have Nickel allergies/sensitivities or have a recommendation from a doctor to avoid any exposure to Nickel or Chromium).
So (again, in my opinion, based on the studies which I have read), the concern for leaching of Nickel (and/or Chromium) into food cooked in stainless is primarily only a concern under atypical/extreme-use scenarios — not under “normal use as intended” scenarios. As always, I invite Lead Safe Mama readers to share any research with me that might contradict this understanding.
Section #3.a.) Caveats — for ensuring you are using Stainless Steel appropriately/safely
Based on the research I have done (including reviewing many of the above-mentioned studies and conducting XRF testing of thousands upon thousands of stainless steel items), it is my understanding that stainless steel is safe for cookware and other food-use items, with the following caveats:
- If you actually have a Nickel allergy — or if your doctor is concerned because you have tested positive for unsafe levels of Nickel or Chromium (in a blood, urine, or hair test), you may want to avoid stainless. Stick with clear glass and well-seasoned cast iron (unless you happen to have Hereditary Hemochromatosis) and — if appropriate/recommended by your doctor — emphasize raw foods in your diet whenever possible.
- Avoid “long-form” cooking of high-acid foods in stainless steel vessels. One specific example (per the study noted above): don’t cook tomato-based products for hours on end (for reduction purposes) in stainless ware. Using stainless (as I do in my home) to quickly sauté vegetables (or to cook pancakes, eggs, or to boil water) should be a non-issue. That said, my current preferred vessels for simply boiling water are clear borosilicate glass (link one and link two), and my preferred “pan” for pancakes is an uncoated vintage cast-iron griddle that spans across two burners.
- In any home (as I have written about previously), cookware should optimally consist of an assortment of materials — (e.g. clear, undecorated glass; plain, enamel-free, undecorated cast iron; and stainless steel). Never rely on just one pan or just one type of pan. Mix things up! I also prefer hand-made unfinished natural wood for utensils, and use those in conjunction with stainless utensils — you can see some examples here.
- If you are choosing stainless cookware for your family, you should purchase the highest-quality stainless steel cookware you can afford. That said, even less-expensive single-component stainless items should not present health concerns as long as caveats #2 and #3 above are followed! In my work, I recommend both inexpensive and expensive stainless options; as long as the items are made of 18/8 base metal (and used as intended), the health impacts should generally be the same.
- Avoid inexpensive insulated stainless steel water bottles — as many of those are sealed using a solid Lead sealing dot (link with details here) and sometimes with much lower quality stainless.
- Stainless steel water bottles should be used only for water (never for coffee, tea, juice, or other acidic beverages), with the water changed daily with rinsing between uses. Link with details here. For water bottles that might hold something other than water, I prefer glass (link with options here).
- Note: many stainless steel cookware vessels also have some non-stainless components (like glass lids with painted logos, cast Aluminum valves, Brass handles, etc.) — these can test positive for unsafe levels of Lead (or other toxic metals), so the considerations here (in asserting that stainless is a safe option) only apply to cookware in which ALL components are stainless steel. A good example of the type of cookware to be wary of is this stainless steel Butterfly brand pressure cooker from India.
- When possible, choosing low-nickel or nickel-free stainless (400 series alloys — also sometimes simply referred to again by the (approximate) percentages of Chromium and Nickel present as “18/0”) is preferable. Here’s a good example of some high-quality low-nickel stainless cookware — link with details here.
Section #4) Is Nickel-free stainless steel really a safer choice?
In our family, we do not have a concern for high-quality stainless steel cookware containing Nickel:
- We intentionally use an assortment of cookware of varying materials, so do not have excessive exposure to any metals through any one particular pot or pan.
- This lack of concern is supported by the fact that none of the six of us — in our nuclear family — has ever tested positive for Nickel at concerning levels, nor exhibited any Nickel sensitivity (with jewelry, for example).
- Additional evidence supports the possibility that high-quality 18/8 stainless is relatively inert in many applications (when used as intended vs. cooking acidic tomato sauce for 20 hours!): stainless steel has long been widely used (for many decades — nearly a century actually, since 1926 — see the image with a link below) for medical devices internally/inside the body, with success.
Even in light of these considerations demonstrating the safety of 18/8 stainless, out of an abundance of caution — given the fact that research is always discovering new potential impacts — it might be worthwhile to consider choosing Nickel-free (or low-nickel) stainless. Maybe opt for using glass alternatives — like water bottles — whenever possible. This is among the many reasons why these low-nickel pans are my favorite for cooking for my family.
Section #5) What about multi-layer construction Stainless Steel pans with a Copper “core?” Or, with an Aluminum “core?”
For stainless pans with a Copper or Aluminum core (the Copper or Aluminum layer is specifically added to the vessel — “sandwiched” between two stainless steel layers — for the purpose of even heat dissipation), the core is normally fully encased between layers of stainless steel and, as it is not exposed, there is no opportunity for the Copper or Aluminum layer to impact the health of the user.
The exception to this common construction for pans with a Copper core is some designs in which the Copper core is visible as a band of Copper showing around the lower edge of the pan (as an accent for decorative purposes, see image below). However, again, this does not impact the food cooked in the pans at all, as it is not a food-contact surface. The image below shows the exposed decorative copper edge on a pan with a copper core. Note: I no longer recommend this brand of pan and am only sharing the image to demonstrate this one point.
Section #6) What about Stainless Steel with measurement markings on the interior surface of the pots or pans?
I have previously cautioned about the concern for the potential for Lead in the food-contact surface measurement markings of stainless pots and pans (see markings on the interior of the cooking pot in the image below). These interior markings are typically either laser-etched or painted-on. Sometimes they are also applied as vinyl decals (typically on the outside of vessels not intended for use with cooking).
While laser-etching is safe, painted or vinyl markings on any food surface are always a potential concern. However, more recent (post-2018) examples of measurement markings I have tested (on stainless steel vessels) have typically not been positive for Lead (this is a good example of that — link). In general, to be certain the markings are Lead-free (in the absence of testing a specific pan you might be interested in), look for etched or molded markings, or for pans with no interior markings on the food surface.
Section #7) But I heard you tested some stainless items and found them to be contaminated with other toxic metals; is that a concern?
Purchasing mass-manufactured products always has risks (possible contamination from manufacturing stream and/or supply chain variations), which is why I do my best to find (and write about) and recommend trusted brands that consistently manufacture products that test negative for Lead, Cadmium, Mercury, Arsenic and Antimony, using XRF technology. It is for this reason (for example) that I only recommend ONE brand of insulated stainless water bottles (link) — as that is the ONLY brand of insulated water bottles that I have found to consistently test negative for toxicants across all recent years of production (specifically negative for the five metals listed in the previous sentence)!
That said, it is incredibly rare to find stainless steel cookware products that test positive (in the metal of the vessel itself — not in a non-stainless component of the product) for Lead, Cadmium, Mercury, Arsenic, or Cadmium. However, recently (in the past year) I did some preliminary testing of two examples of pots/pans from one company (each example likely manufactured after January 2021), which tested positive with preliminary testing for trace levels of Mercury in the food surface. This is the first time I have ever found traces of Mercury in a stainless product! In response to these preliminary findings, I did a deep dive of research and confirmed it is actually possible for Stainless Steel to be contaminated with Mercury. I will be writing about that more (in detail) shortly — and will link that article here as soon as it is live.
Earlier products from this same company (tested and manufactured before 2021) have all tested negative for Mercury, so this potential “Mercury contamination” (if it can be confirmed with additional testing!) is likely a batch-specific problem. In response to this preliminary testing, and pending additional third-party testing, I removed this brand (All-Clad) as a current recommendation in my store and shopping site and am working on doing additional testing to confirm whether or not other testing methodologies (i.e. other than XRF testing) might confirm trace Mercury in these pans — or if it is some sort of anomaly in the readings. And, if so, what might cause the anomaly (in rare instances, a combination of other metals will produce a reading — in the GUI interface on the XRF instruments — for a third metal that is not actually present, and I definitely need to rule this out). In the meantime, if you have All-Clad stainless steel products purchased before 2020, I would not be concerned; if you have All Clad stainless steel products purchased after 2020, I would consider setting them aside for the moment until additional independent testing can be done to determine whether or not some of the pans may have low-level mercury contamination in the stainless, and (if so) what the batch-range is (the date-range of manufacture and product-range) for that potential contamination.
Note: one member of one of the families who owned one of the two pans in question was tested for metals and reported to me that their metals test was negative for Mercury.
Section #8) In Conclusion
The work of Lead Safe Mama, LLC is designed to educate our readers about the science behind any issues and considerations for any particular topic. Unfortunately, while science is the right place to start an inquiry, a lot of “science” (e.g. non-peer-reviewed studies, popular articles, etc.) is biased, and/or imprecise, ambiguous (depending on the intentions, origin, and funding behind any given study). Further/additional/more rigorous inquiry is often necessary.
With the conversation and considerations above about Stainless Steel, we are trying to give our readers as many of the answers to this inquiry as possible — in one place — so you can therefore move forward in making safer choices for your family. Ideally, we must acknowledge that industrially-manufactured manmade materials are inherently not “natural,” and therefore not always safe. On a practical level, we often have to choose between “lesser evils” and evaluate those choices based on particular considerations for our family (and the advice of our doctors). My family has chosen to continue to use stainless steel and currently do not have concerns (in general) with stainless steel toxicity.
In evaluating my comments above about long-form cooking, I reflected on the fact that I used to often make fruit jams/preserves in the summer (plum, blackberry, etc.) and that those are long-form cooking. I no longer do that — as concentrated sugars are not great for humans, and eating fresh fruit is preferred — but I don’t have a concern with using jam in moderation now and then (not as a primary food staple). If I were to make a sandwich, I prefer almond butter and honey (for example) noting the honey is lightly-filtered, uncooked, and raw, with fewer opportunities for contamination from processing. This is a complicated journey and most choices and considerations impact others. In the end, you have to do what you decide is best for your family — and that includes factors of time and convenience. But if just one reader (you?) can make those choices from a more educated standpoint (instead of just assuming that products sold to us by manufacturers are automatically safe) then the movement will have a small win for the future.
For those new to this website:
Tamara Rubin is a multiple-federal-award-winning independent advocate for childhood Lead-poisoning prevention and consumer goods safety, and a documentary filmmaker. She is also a mother of Lead-poisoned children (two of her sons were acutely Lead-poisoned in 2005). Since 2009, Tamara has been using XRF technology (a scientific method used by the U.S. Consumer Product Safety Commission) to test consumer goods for toxicants (specifically heavy metals — including Lead, Cadmium, Mercury, Antimony, and Arsenic). All test results reported on this website are science-based, accurate, and replicable. Items are tested multiple times to confirm the test results for each component tested. Tamara’s work was featured in Consumer Reports Magazine in February of 2023 (March 2023 print edition).