For products that fall into the cosmetics category, the ingredient list is several lines of text on the back of a product package, ordered by weight. For example, if water is the first ingredient in a list, then it means that water is the highest percentage ingredient making up that formula. Then the ingredient after water is the second most used ingredient, and so on.
A caveat to this rule is that ingredients making up below 1% of a product formula can be listed in any order. This is why preservatives or colorants are often listed last, or close to last, since they’re used at very low concentrations.
Very helpful reading and info, thanks.