Stability and dermatological safety assessment of Cryptocarya alba (Peumo) and Laureliopsis philippiana (Tepa) essential oil-carrying dry shampoo formulations for dermal use in dogs.

Abstract

Introduction: Antibiotic resistance is a major concern in human and veterinary medicine, supporting the development of alternative topical products for companion animals. This study aimed to develop and evaluate essential oil (EO)-based dry shampoo formulations incorporating EOs from Cryptocarya alba and Laureliopsis philippiana as potential veterinary dermocosmetic platforms for canine skin care and complementary management of superficial pyoderma.

Methods: Starch-based dry shampoo prototypes containing C. alba or L. philippiana EOs were developed using corn starch, tapioca starch, or their mixtures. Magnesium stearate (MgS) was evaluated as a functional excipient, and two mixing protocols were compared. Optimized formulations were subjected to physicochemical characterization, thermal, mechanical, and 9-month stability assessments, and in vitro antibacterial testing against Staphylococcus pseudintermedius. Preclinical dermal safety was evaluated in BALB/c mice through macroscopic irritation scoring, body weight monitoring, and histological analysis. Subsequently, an exploratory, randomized, controlled, blinded, four-arm parallel-group study was conducted in 32 client-owned dogs with superficial pyoderma allocated to receive SLP, SCA, vehicle shampoo, or a chlorhexidine-based reference treatment for 21 days.

Results: MgS improved formulation homogeneity, fluidity, and reduced agglomeration, while the selected mixing protocol enhanced overall powder performance. The optimized formulations showed preliminary physical stability, although progressive changes in texture, fluidity, agglomeration tendency, and aroma were observed during storage. In vitro antibacterial activity was assay-dependent: no measurable inhibition zones were observed by agar diffusion, whereas serial dilution and viable-count assays showed concentration-dependent reductions in bacterial recovery, including effects associated with the vehicle formulation. No macroscopic or histological signs of dermal irritation were observed in mice. In dogs, the formulations were well tolerated under the evaluated conditions. Microbiological outcomes differed numerically among groups but not significantly; among the EO-containing formulations, SCA showed the most favorable exploratory profile, including culture negativity in 3/8 dogs and the highest proportion of dogs reaching a non-significant bacterial burden.

Discussion: These findings support the feasibility of incorporating C. alba and L. philippiana EOs into starch-based dry shampoo prototypes and provide preliminary evidence of physical stability and dermal tolerability. However, the assay-dependent antibacterial response, alkaline formulation pH, limited batch replication, and exploratory clinical design preclude conclusions regarding clinical efficacy. Further studies should include formulation optimization, quantitative chemical stability assessment, dermal permeation studies, and larger randomized controlled clinical trials.