Squalane is a hydrogenated, stable form of squalene — a lipid that's naturally present in human sebum and makes up a meaningful portion of the skin's own oil production. Because it so closely resembles the skin's native lipids, it's absorbed readily, sits comfortably on all skin types, and doesn't trigger the comedone formation associated with heavier oils. Modern squalane is almost always derived from sugarcane (plant-derived) rather than shark liver oil, which was historically the source.
What distinguishes squalane from other facial oils is its stability and skin similarity. Unlike vitamin C-rich oils that oxidize quickly, or heavy oils that sit on the surface and potentially clog pores, squalane is chemically inert, long shelf-life, and behaves predictably. It's primarily an emollient — it softens skin and reduces transepidermal water loss — rather than a delivery system for actives. This makes it a finishing-step oil rather than an early-routine ingredient.