Ectoine–Vehicle Contrasts After Four Laser Stressors Vary Across Response Domains and Laser Procedures: An Exploratory Secondary Analysis of a Randomized Factorial Study

Ectoine is used in peri-procedural skincare, but its effects may vary with laser procedure, concentration and application timing. This exploratory secondary analysis examined 360 ectoine–vehicle contrasts from a randomized within-participant décolletage study involving 30 adults with Fitzpatrick phototype II. Vehicle and 1%, 5% or 7% ectoine formulations were applied before (PRE) or after (POST) fractional CO2, Er:YAG, 1064 nm Nd:YAG or picosecond 532 nm Nd:YAG exposure. Corneometry, transepidermal water loss (TEWL), erythema, melanin index and skin-surface pH were assessed immediately, at 24 h and at 14 days. Of 360 contrasts, 113 (31%) were significant after the Holm adjustment. Among 23 significant TEWL contrasts, 18 indicated lower values with ectoine; for Er:YAG, 7% POST at 24 h, the difference was −22.71 g/m2/h (95% CI −30.93 to −14.50). Cross-laser directional heterogeneity occurred in 59/90 configurations (65.6%), non-monotonic concentration patterns in 74/120 (61.7%), and PRE/POST sign reversals in 83/180 (46.1%). These descriptive patterns did not establish a consistent dose–response relationship. Effects differed across response domains and laser procedures, but exploratory comparisons cannot establish chromophore-specific mechanisms or improvements in healing or downtime.