Is it safe to use a slow cooker on high all day?
Use caution. The bigger issue is the ceramic insert, especially if it is old, cracked, imported, or unverified.
What's actually in it
Most slow cookers use a glazed ceramic insert. The temperature setting matters for food safety and cooking time, but the material question is about the glaze.
A modern, intact, lead-free slow cooker is usually a reasonable kitchen tool. Be more cautious with older inserts, chipped glaze, imported pieces with no lead-free claim, and long acidic recipes like tomato sauce or vinegar-heavy dishes.
What the research says
A 2025 study in J Hazard Mater measured cadmium and lead migration from ceramic mugs over 24 hours using 4% acetic acid. Interior migration stayed within current EU limits, but exterior lip areas with some decorative pigments released higher levels.
A 2021 study in Food Chem Toxicol tested migration from food-contact plastics using food simulants, including acetic acid for acidic foods. It found low concern under the tested regulatory conditions, but it shows why acid and long contact are part of food-contact testing.
For slow cooking, use an intact modern insert, avoid chipped glaze, and do not store acidic leftovers in the crock. If you cook tomato-heavy meals often, stainless steel pressure cooking is the cleaner routine.
The research at a glance
| Study | Journal | Year |
|---|---|---|
| Migration kinetics of cadmium and lead from ceramic mugs. | J Hazard Mater | 2025 |
| Migration of substances from food contact plastic materials into foodstuff and their implications for human exposure. | Food Chem Toxicol | 2021 |
What to use instead
Shop kitchen swaps made with stainless steel, glass, wood, and ceramic.
Shop Non-Toxic Kitchen