How do ingredient + allergen filters work on PLPs?

Magento layered nav handles this cleanly with the right attribute design:

• Per-ingredient boolean attributes — contains_paraben, contains_sulfate, contains_fragrance, contains_gluten, contains_silicone, etc. Layered nav exposes “Free from” filters.
• Positive flags — is_vegan, is_cruelty_free, is_reef_safe, is_pregnancy_safe, is_clean_beauty. These tend to outperform “free from” framing for SEO and conversion.
• Customer profile allergens — logged-in customers save up to 5 allergens. Magento auto-warns on PDPs that contain them (red banner). Wishlist / cart adds blocked with a confirmation modal.
• INCI catalogue as a structured attribute (one source of truth for ingredient list, allergen flags, regulatory fields).

Performance note: with 30+ filter attributes on a 5,000 SKU catalogue, you’ll need Elasticsearch / OpenSearch (not MySQL native search). Magento ships ES out of the box from 2.4.x.