Safety Evaluation of Fine Bubble Shower Washing for Patients With Atopic Dermatitis: A Double‐Blind, Randomized, Prospective Crossover Clinical Trial

Atopic dermatitis (AD) involves chronic eczema resulting from barrier dysfunction. Fine bubble (FB) technology generates microbubbles (< 100 μm) and ultrafine bubbles (< 1 μm) for surfactant-sparing cleansing. We assessed the short-term safety of an FB shower in AD. In this double-blind, randomized, crossover study, adults with mild AD completed two 2-week periods separated by a 2-week washout in sequence. Bathing instructions and petrolatum moisturizer use were standardized and enforced. The Eczema Area and Severity Index (EASI) was scored using whole-body photographs by a blinded team. Transepidermal water loss (TEWL) and stratum corneum hydration were measured on Days 0, 14, and 28. Because baselines were unavailable for the second 2-week period, the primary analysis compared Day 0-14 changes between groups using baseline-adjusted analysis of covariance; Day 0-28 changes were also explored. The primary outcomes were EASI changes; TEWL and hydration were the secondary outcomes. Groups used a conventional shower (control) first and then FB shower second or vice versa (once each). Twenty-three participants were analyzed (mean age 40.9 ± 8 years; 83% male). Day 0-14 EASI changes did not differ between FB and control (0.62 ± 2.21 vs. 0.05 ± 0.68; F = 0.93, p = 0.35). EASI changes to Day 28 were nonsignificant (0.02 ± 1.65 vs. -0.03 ± 1.02; p = 0.90). TEWL changes for Days 0-14 (0.31 ± 4.75 vs. 1.09 ± 6.21 g/m²/h) and to Day 28 (5.49 ± 14.43 vs. -0.27 ± 5.28 g/m²/h) showed no between-group differences. Hydration changes were similar for Days 0-14 (5.53 ± 13.23 vs. 6.14 ± 7.96 AU) and to Day 28 (18.41 ± 10.33 vs. 21.09 ± 11.07 AU). No serious adverse events or discontinuations for worsening symptoms occurred. Under standardized, low-irritant conditions, the FB shower was well-tolerated by adults with mild AD and did not worsen severity or barrier indices over 4 weeks. However, the superiority of FB to a conventional shower was not demonstrated.