Never use soap on cast iron
Among the most confidently held rules in domestic cooking, and the manufacturer contradicts it outright. The prohibition outlived the soap it was formed around.
What is claimed
That washing a seasoned cast iron pan with soap or washing-up liquid strips the seasoning, and that it should be cleaned with water and salt or a brush alone.
Where this comes from: Traditional household practice.
Does it work?
Does not work
Refuted on the manufacturer's own published guidance, which is unusually good evidence here: a cookware manufacturer has every commercial reason to be conservative about how its products are cleaned, and it is being LESS restrictive than the folklore. A bias argument runs the wrong way for the claim.
This is a verdict on whether the technique is effective. Whether it is safe on a particular surface is a separate question, answered below.
Where not to use it
Seasoned cast iron
Unsafe
Do not do this. The risk is established, and it is described below.
The practices this myth pushes people towards are the harmful ones. Soaking a pan to avoid using detergent, or leaving it to air dry, are both named by the manufacturer as causes of rust — so following the folklore actively increases the risk it was invented to prevent.
Precautions
- Check the manufacturer's instructions
Why it works
The claim's reasoning is that seasoning is a layer of oil and that soap is designed to remove oil, so soap must remove seasoning. The premise about soap is right and the premise about seasoning is not. Seasoning is not oil sitting on the metal — it is oil that has been polymerised by heat into a hard, cross-linked layer chemically bonded to the iron, which is why it survives cooking. Surfactants lift free oils by emulsifying them; they have no mechanism for breaking the cross-links in a polymerised film. The historical version of the claim was sound because lye-based soaps worked by saponification and alkaline attack, which does degrade such a layer, and those are not what is in a bottle of washing-up liquid.
Background
Almost everybody who owns a cast iron pan has been told this, usually with some force, and it has the shape of hard-won knowledge passed down. Lodge, which manufactures the cookware, states the opposite in its own care guidance: soap is acceptable, because the soap used for washing dishes today is no longer strong enough to remove seasoning, and it is an easy way to prevent build-up. The rule was not invented. It was formed when household soap meant genuinely caustic lye-based products that would strip a polymerised oil layer, and it simply outlived them. What the manufacturer does prohibit is water in prolonged contact: the dishwasher removes seasoning and will likely cause rust, and soaking is described as a recipe for rust. So the folklore is not wrong about there being a rule — it has attached the rule to the wrong variable. The thing to fear is standing water, not detergent.
Conditions
- Wash by hand, not in a dishwasher
- Do not leave the pan to soak
- Dry completely straight afterwards, then oil thinly
What it does not do
- It says nothing about strongly alkaline products, which are a different matter entirely and are not what the claim is about
- The manufacturer's guidance covers its own seasoned cookware; enamelled cast iron is a different material with separate guidance
- The real risk the folklore is pointing at — water left in contact — is genuine, and following the myth by soaking the pan instead is worse than using soap
What to use instead
- Detergent — A surfactant-based cleaner. The general-purpose answer for greasy and particulate soil, and the correct first choice far more often than any specialist product.
- Rinsing and drying — The step people skip, and the one that decides whether cleaning protected the surface or damaged it. Residue left behind is exposure that continues after you stop.
Evidence
Does not work
Refuted on the manufacturer's own published guidance, which is unusually good evidence here: a cookware manufacturer has every commercial reason to be conservative about how its products are cleaned, and it is being LESS restrictive than the folklore. A bias argument runs the wrong way for the claim.
Sources
How to Clean seasoned cast iron
Lodge Cast Iron (Lodge Manufacturing Company) · Manufacturer documentation
Relied on for: That soap is acceptable on seasoned cast iron because modern dish detergent is no longer strong enough to remove seasoning, that the dishwasher removes seasoning and likely causes rust, and that soaking is a recipe for rust. (states this directly)
Verification: a person has read the passage relied on.
Read on — The three-step cleaning method, the soap statement, and the rust guidance. Supports a wider statement — our claim was widened. Created the cast iron record and overturned the most widely repeated rule about it: CleaningHQ would otherwise have carried the folk prohibition on soap, and the manufacturer states the opposite with the reason. SPRINT 32 READ THE FAQ BLOCK AND IT ADDED ALMOST NOTHING — soap, soaking, steel wool and the dishwasher again, in question form. The three cast-iron rows it unblocked were unblocked by re-reading OUR OWN STALE NOTES, not by reading more of this source.
Last reviewed by a person on .
Last reviewed by a person on .