Prop 65, allergen and EU AI Act labels: a product warning guide for online stores

Key takeaways

• California Prop 65 requires clear warnings for products that can expose people to listed chemicals.
• In the EU and UK, allergen information for food must be available before an online purchase is completed.
• The EU AI Act may require disclosure for certain AI-generated content, and labelling it is good practice.
• EU AI Product Warnings & Labels shows the right label on the right product, by state or country.

Why warnings belong on the product page

A warning in your terms or on the packaging is often not enough. Many rules expect the customer to see the information before they buy. For an online store, that means on the product page or before checkout.

Showing labels clearly also builds trust. Shoppers with allergies, parents and cautious buyers look for this information, and they buy with more confidence when they find it.

California Proposition 65

Proposition 65 is a California law that requires businesses to warn people about significant exposure to chemicals on the state's list of substances known to cause cancer or reproductive harm. The list includes hundreds of chemicals found in everyday products, from some plastics and metals to wood dust.

If you sell products that may contain listed chemicals to customers in California, you may need a "clear and reasonable" warning. For online sales, the warning is usually shown on the product page or another place the customer sees before buying. The duty follows where the product is sold to, and visitor location is only approximate, so many stores show the warning by location on the product page and also before purchase for orders shipping to California.

Allergen information for food

In the EU and UK, most mandatory food information, including the 14 major allergens, must be available to the customer before an online purchase is completed. Allergens are commonly shown on the product page in a clear, highlighted label so shoppers can check them at a glance.

EU AI Act transparency labels

The EU AI Act introduces transparency duties for certain AI-generated or AI-manipulated content, so people know when they are dealing with AI. Whether a specific use in your store needs a disclosure depends on the case, but if you use AI-generated images, descriptions or products, a clear label is good practice and keeps you open with customers.

This guide is general information, not legal advice. Check which rules apply to your products with a qualified adviser.

How to write a clear warning

Whatever the rule, good warnings share a few qualities:

• Visible. Place the label near the price or Add to cart button, not at the bottom of a long description.
• Readable. Use a size and colour that stand out, and keep the text short.
• Specific. Name the chemical, allergen or AI use the warning is about where the rules require it.
• Consistent. Use the same wording and style across all affected products.

Labelling mistakes to avoid

• Warning on every product. Over-warning makes labels easy to ignore. Show them only where they apply.
• Hiding the warning in a tab. Customers should not have to click to find important safety information.
• Forgetting variants. If only one colour or size contains a listed chemical, label that variant clearly.
• Not updating labels. Review your labels when suppliers, ingredients or rules change.

Example: one store, three labels

A homeware store based in the UK that ships worldwide. It sells ceramic mugs, scented candles and a small range of chocolate gifts. Some glazes on the mugs contain lead compounds, the chocolate contains milk and nuts, and the product photos for a new range were created with AI.

The store needs three different labels. California visitors see a Prop 65 warning on the mugs. Every visitor sees the allergen label on the chocolate, with milk and nuts highlighted. The new range carries a short note that its images were generated with AI.

With location rules, each shopper sees only the labels that apply to them, and every label sits next to the price where it cannot be missed. The rest of the catalogue stays clean, and the team updates labels in one place when products change.

How to show labels by location

EU AI Product Warnings & Labels adds Prop 65, allergen and EU AI Act labels to your product pages, and can show them by state or country. That means California visitors see a Prop 65 warning, while customers elsewhere see the labels that apply to them.

1. Install the app from the Shopify App Store.
2. Create a label for each warning type you need.
3. Choose the products each label applies to.
4. Choose the states or countries where each label should appear.
5. Preview product pages from different locations to check the result.

See how this fits with the other Effectify apps on our Security & compliance page.

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Written by the Effectify team, the developers and support staff who build and maintain Effectify's apps. Last updated 20 October 2026. Questions about this guide? Contact us.