Moisturizing and repairing effects and mechanism of pullulans with different molecular weights on hair

Chemical treatments and ultraviolet radiation exacerbate hair damage and moisture loss, driving the need for effective repair strategies. Pullulan, a natural polysaccharide from Aureobasidium pullulans, offers excellent water solubility and film-forming properties. This study evaluated pullulan of low (LMW, 10 kDa), medium (MMW, 200 kDa), and high (HMW, 2000 kDa) molecular weights (Mw) for hair repair and scalp protection. At 2% concentration, reparative efficacy showed significant Mw dependence. On healthy hair, HMW pullulan reduced friction by 41.5% via superior surface film formation but remained localized to the cuticle. MMW pullulan balanced permeation and structural stability, enabling penetration into the cortex. In UV-damaged hair, MMW pullulan performed best, restoring moisture by 35.5%, increasing tensile strength by 40.6%, and ameliorating cuticle damage. Mechanistic studies revealed that pullulan acts primarily through hydrogen bonding rather than disulfide bond regeneration, as confirmed by urea disruption and thiol quantification. ATR-FTIR, DSC, and ITC further suggested that pullulan reinforces the keratin network via hydrogen-bond-mediated physical infilling and stabilized water binding. Additionally, in vitro assays showed that MMW pullulan alleviated H₂O₂-induced oxidative stress in HaCaT cells by reducing ROS and downregulating pro-inflammatory cytokines (IL-1β, TNF-α, IL-6). These findings demonstrate potential cytoprotective effects on scalp keratinocytes in vitro, supporting its development as a dual-action ingredient for both hair and scalp care.