Nylon-12 Nylon! As we say in the review of the product which contains this, we’re not sure what this well-known synthetic ingredient is doing in a product that was promoted to us as natural – but many products that feature in our book are a combination of botanical ingredients with synthetics – in this case, nylon (not dissimilar to the type used in crackling sheets and old-fashioned school blouses!) Usually found in mascaras (to lengthen lashes), this can however cause allergic reactions.