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Steel Guide

By Meg Christensen | Updated June 2025

If you've ever wondered whether your stainless steel pots are safe or why some people react to them, you're not alone—steel is one of the most common yet misunderstood materials in our kitchens. Made from combinations of naturally occurring metals like iron, carbon, chromium, and nickel, steel cookware is generally very safe, though it may affect the 11-16% of people with nickel sensitivities. Here's everything you need to know about the different types of steel, what metals they contain, and how to choose the right cookware for your specific health needs.

Jump to: Rating scale for steel | What is stainless steel made from and is it safe? | What is carbon steel vs cast iron and how are they different than stainless steel? | How and why I use the words toxic, non-toxic, and chemical

What is in stainless steel?

What is steel made of?

All types of steel are a mixture of two naturally occurring metals, iron and carbon. The difference between types is how much iron or carbon is present, and whether they’re mixed with other metals or elements, like silicon, chromium, or nickel.

Steel is an umbrella term that covers cast iron, carbon steel, and stainless steel.

What is an alloy?

Alloys are combinations of metals. Metals are combined to make a stronger, less corrosive, or less chemically reactive material than each individual metal would be.

What is stainless steel made of?

Stainless steel is almost always a mixture of iron, carbon, chromium and nickel. There are about 60 different types of stainless steel, based on slightly different blends of metals. Stainless steel is often categorized by how much chromium and nickel it contains:

What is 18 10 stainless steel? It contains 18% chromium and10% nickel, and you’ll see it marked as 18/10. Is 18 10 stainless steel safe? Yes, as long as you aren’t allergic to nickel or chromium. This is very commonly used in cookware.
What is in 304 stainless steel? It contains 18% chromium and 8% nickel, and is also called18/8 stainless steel. Is 18 8 stainless steel safe? Yes, as long as you aren’t allergic to nickel or chromium. This is very commonly used in cookware.
What is stainless steel18 0? It contains 18% chromium and no nickel, but it is weak, and corrosive, so would need to be blended with titanium to be used in cookware. It’s uncommon, but you’d see it labeled as 18/0.
What is stainless steel 316? T-316 stainless steel is 6% chromium, 10% nickel, and 2% molybdenum. It’s also called surgical grade because it’s very resistant to corrosion, due to the molybdenum. It is safe to cook with.

Why is there nickel in stainless steel?

Nickel makes steel more formable when it’s being made into pot shapes, and once its formed, also adds strength and resistance to corrosion.

Why is there chromium in stainless steel?

It strengthens steel, and makes it more resistant to corrosion. It also gives it a shinier finish that looks nice— this is why a lot of people have stainless steel appliances throughout their kitchen.

Is stainless steel toxic?

No, it is a very safe material. You may be cautious using it if you have an allergy to chromium or nickel. If you have an allergy to nickel, there are nickel-free stainless steel options available for cookware— see the ones I recommend on my cookware and bakeware pages (both are part of Look Inside.)

Are stainless steel saucepans safe?

Yes! You may be cautious using them if you have an allergy to chromium or nickel. If you have an allergy to nickel, there are nickel-free stainless steel options available for cookware— see the ones I recommend on my cookware and bakeware pages (both are paywalled.)

Is chromium toxic?

No, not in the context of stainless steel cookware or home goods. But, some people are sensitive to it, and certain forms of it are not good for people.

Chromium 0, also known as metallic chromium, is the type of chromium used in stainless steel cookware and home products. It is known to leach out in tiny quantities from stainless steel during cooking, and there are no known health issues associated with this, unless you have an allergy to chromium— in that case, it can cause dermatitis (skin rash.) An estimated 1-3% of the population has an allergy to chromium.

Chromium III, also known as trivalent chromium, or chromium 3, is essential for life. It is in food, water, and most vitamins.

Chromium IV, also known as hexavalent chromium, or chromium 6, is the synthetic version, and is toxic. Importantly, it is not used in pots and pans and so does not leach into food! It is plated onto other metals like stainless steel to form the shiny protective coating that looks nice on appliances. However, it’s chemically inert once it’s plated on a surface — it is safe to touch and use. However, it is a problem for the industrial workers breathing it in during manufacturing because it’s known to cause cancer and other health issues with the airway, skin and eyes, as well as with the organs that work to remove it from the body— the liver and kidneys. Chromium IV is also what the movie Erin Brockovich was about — waste from manufacturing does get into the water supply. It is being phased out because of this; in California it will be banned for all uses by 2039.

Is nickel toxic?

No, generally not, with some caveats.

11-16% of people have a sensitivity to nickel. Nickel occurs naturally in many foods including flours, seeds, beans, and chocolate— and eating it can cause allergic contact dermatitis (skin rashes) after ingestion that show up anywhere on the body. You can also ingest it by cooking with stainless steel that contains nickel— it does leach in very small amounts from the walls of the cookware into the food. Finally, touching it, as with nickel jewelry, can also cause a rash in sensitive people. So, if you are sensitive, it may be worth using nickel-free cookware and coffee/teaware. (Personal note: I’m allergic to nickel and switching helped me so much! So much less mystery eczema, oh my gosh.)

The other caveat is that like chrome, nickel is harmful to workers, and being exposed to nickel refinery dust can lead to lung and nasal cancer from breathing it in at high amounts over time. It is not harmful to you, the end user, and our bodies are very good at excreting what we ingest every day. The upper tolerable limit of nickel we can ingest daily is 1,000ug, and adults on average ingest 69-162ug of it daily. Like aluminum, or sunshine, nickel is a normal part of our diets that our bodies know what to do with, and we do not need to avoid it as strictly as we need to avoid things like lead or PFAS. Read more about how I think about aluminum here, and lead here.

Does nickel leach out of pots?

Yes. When you simmer food, especially acidic food, for long periods of time, in regular stainless steel, the heat and acidity encourages leaching of the nickel from the pot into the food. It’s most pronounced during the first 6 uses (yes, there is a study), and it tapers off after that. If you’re not sensitive to nickel, it isn’t a health concern.

Is there lead in stainless steel?

No. Luckily, it is not part of the alloy mixture!

Read on for more, or jump back up to the menu

Non Toxic Coffee Makers

Nickel Free Cookware (Part of Look Inside)

Cast iron vs carbon steel

What is cast iron made of?

Cast iron is a type of steel that is mostly iron, but also contains more than 2% carbon, and usually around 1% silicon. Silicon is a natural mineral, is chemically inert, and non-toxic. It’s used to make cast iron pans moldable during production, and is not the same thing as silicone, which is a synthetic polymer that uses silicon as an ingredient.

What is carbon steel made of?

This is confusing, but carbon steel contains less carbon than cast iron. It contains about 1% carbon (while cast iron contains between 2-4% carbon.) It can also contain manganese, phosphorus, sulfur, and silicon.

Is cast iron safe to cook with?

Yes, it’s a very safe material for the majority of people. The exception would be if you have hemochromatosis, a genetic disorder where your body stores too much iron. That’s because some iron can be transferred from the pot into food. Because of this, cooking with cast iron can actually be a helpful way to get some additional non-heme iron into your diet if you are anemic, though it isn’t generally enough to correct a deficiency. That’s because non-heme iron is not as bioavailable as heme iron and the amount transferred is small, depending on what you are cooking. If you are concerned about hemochromatosis or anemia, you can check with your doctor about avoiding or using cast iron.

What is silicon?

Silicon is a metalloid— it’s an element that’s in between a mineral and a metal. It’s the 8th most abundant element on earth, and it’s usually found in it’s oxide form as sand! Silicon is considered possibly essential in human nutrition, and it’s used to make bricks, glass, porcelain, and ceramics. It’s added into the mixture when making cast iron so that the thin pieces are easier to form.

What is silicon vs. silicone?

Silicon is the naturally occurring metalloid, whereas silicone is a synthetic material made with a combination of silicon, oxygen, and a variety of other elements to make plastic-like, rubbery substances, lubricants, adhesives, and other materials.

Does cast iron have lead?

No.

Read on for more, or jump back up to the menu

Steel Bed Frames

Non Toxic Slow Cookers and Dutch Ovens (Part of Look Inside)

About “Non Toxic” and Other Language

A quick note about how I use the terms non-toxic, chemical, and toxin:

I understand that there is no agreed-upon definition of the term non-toxic, and that everything, even water, is made of chemicals, so nothing is truly chemical-free. Likewise, I’m aware that toxin refers to a natural substance like a plant poison or venom, whereas toxicant is a more accurate term for the chemicals in products that have a negative health impact. I choose to use these words anyway because they are currently the most culturally agreed-upon, descriptive, and accessible terms that allow people to find the information they are seeking.

Some people really care about the accuracy of this terminology, so I’m letting you know!

Steel Ratings

A rating scale for steel products, which includes cast iron, carbon steel, and stainless steel. Scales keep me consistent and unbiased as I rate and rank products in the Interior Medicine shop, and hopefully they’re helpful for you, too.