Some of the gap can be real; most of it usually isn't — and an ingredient list alone can't tell you which, so here's the honest breakdown.
What an INCI list hides: exact percentages (order only tells you rough ranking, and below 1% ingredients can be listed in any order), ingredient grade and purity, and the formulation work — emulsion stability, texture, how it wears under sunscreen. Two nearly-identical lists can genuinely differ in feel. So the $38 product could be better made. Could.
What the price gap usually is: packaging, fragrance-of-brand, and marketing position. Moisturizers are a mature category — the humectant-plus-occlusive architecture is well understood and cheap to execute well (https://www.ncbi.nlm.nih.gov/books/NBK545171/), and several of the most dermatologist-recommended moisturizers on earth are drugstore-priced. For bland, well-formulated moisturization, price correlates weakly with performance.
How to actually decide: buy the $12 one first. Judge it on the things a list can't show — does it sting, does it pill under SPF, does your skin feel comfortable at hour eight. Hydration benefits show up fast, so a week or two tells you most of what you need. If it disappoints on texture or wear, the $38 one is still there, and now you're paying for a demonstrated difference instead of an imagined one.
And a standing rule that will save you money for years: spend down on moisturizer and cleanser, spend up (if anywhere) on the products where formulation genuinely gates performance — sunscreen you love wearing daily beats every luxury cream in the store. Our /compare and /dupes tools can put the two lists side by side properly.