A serum and cream moisturization regimen outperforms separate use in sustaining hydration, reducing <scp>TEWL</scp> , and balancing surface lipids over an 8‐h study

Skin hydration can be achieved through complementary mechanisms in skincare formulations. Humectants retain water, while emollients and occlusives reduce transepidermal water loss (TEWL) by reinforcing the epidermal barrier. Although consumers follow skincare routines, biophysical comparisons of single-product use versus regimen use across parameters such as hydration, TEWL, and sebum content are limited. Our study measured these parameters in 123 volunteers randomized into four treatment groups: Facial Cleanser (FC) control, Hyaluronic Acid Serum (HAS) group, Moisturizing Cream (MC) group, and Routine comprising HAS followed by MC. Corneometry, TEWL, and sebumetry were measured at baseline, 30 min, and 8 h after treatment application. Corneometry results at 30 min showed that HAS, MC, and Routine increased hydration when compared with FC. At 8 h, only the Routine remained higher than FC. Additionally, TEWL decreased at 30 min for HAS, MC, and the Routine versus FC, whereas at 8 h, only HAS remained lower than FC. We measured sebumetry because skin surface lipids support the epidermal barrier and thus maintain water homeostasis. FC reduced sebum at 30 min due to sebum stripping. However, at 8 h, the Routine's sebum measurements stayed closest to baseline and were lower than HAS and MC individually. Apart from objective measurements, perceived hydration was assessed by a subjective questionnaire. Volunteers who applied the routine reported greater immediate and long-lasting hydration than those who applied HAS or MC individually. These results suggest that layering the Routine improved hydration durability with barrier-relevant water-retention benefits over an 8-h wear period.