Silicone bakeware – Though marketed as inert, repeated high-heat exposure can release small amounts of fillers, dyes, or by-products (especially from low-quality silicone).

Silicone baking mats – Same concern as silicone bakeware; coatings and fillers can break down at high temperatures over time.

Ceramic or stoneware of unknown quality – Glazes may contain lead or cadmium, especially in older or imported pieces. Even “food-safe” glazes can leach trace metals under high heat or acidic foods.

Non-stick coatings on sheet pans – PTFE or ceramic-based nonstick layers can degrade at baking temperatures, releasing fumes or micro-particles.

Decorative foil liners – Often dyed or printed with metallic or colored coatings; under high heat and moisture, these finishes can transfer chemicals or metals into food.

Aluminum foil – Bare aluminum can react with acidic or salty foods during baking, transferring aluminum into food; nonstick foil also carries a chemical coating.

Bare aluminum bakeware (muffin tins, sheet pans, cake pans) – Direct contact with batters or acidic ingredients can cause aluminum to leach; anodized aluminum is more stable but still not ideal at high heat or with acidic foods.