Regarding sunscreens, Hyal Reyouth Moist Sun by the Korean brand Dr. Ceuracle is the most cosmetically elegant sun essence I have ever tried. It boasts SPF 50+, PA++++, chemical filters (no white cast) and is very pleasant to the touch and smell, not at all a sensory nightmare.

Concerning the efficacy of hyaluronic acid (HA) in enhancing skin hydration, I would like to highlight glycerin (glycerol) as a superior humectant. 

Recalling the 500-Dalton rule, which postulates that any compound with a molecular weight inferior to five hundred daltons possesses the ability to penetrate the skin barrier, we can provide a framework that elucidates the mechanisms of penetration of both compounds. Notably, glycerin has a molecular weight of 92.09 daltons, while even a low-molecular-weight HA weighs a substantial 50,000 daltons. For comparison, high-molecular HA can reach a staggering 1 million daltons.

Consequently, HA is rendered incapable of traversing the deeper skin layers and confined to the epidermis. Topical HA is potent and can bind to colossal amounts of water, proving to be a stellar humectant. Nevertheless, the hygroscopic nature of HA can be problematic in dry climates: HA can extract moisture from adjacent skin cells, inducing transepidermal water loss.

A thorough examination of the hyperbolic marketing surrounding this compound reveals a propensity to obscure the boundaries of its categorization concerning its weight, thereby precipitating a conflation of topical HA and injectable HA, which in turn yields imprecise buzzwords such as "filler" printed on topical moisturizers. A comparative evaluation reveals that the rejuvenative effects of topical HA, when contrasted with its injectable counterpart, are eclipsed in terms of its ability to enhance skin volume and elasticity.

Now, glycerin, on the other hand, has consistently demonstrated superior results at a more economical price point. The trihydroxylated glycerol molecule is widely regarded as one of the most (if not best) humectants: its small molecular weight allows it to penetrate the skin effectively, which characterizes its ability to retain and attract water molecules, and ensure long-lasting hydration. 

The synergistic effect of HA and glycerin may provide enhanced hydration benefits by targeting different aspects of skin moisture retention: the concomitant use of both compounds in this study has yielded favorable outcomes.