Companion animal health, like human health, is shaped by dynamic interactions among the genome, exposome, and microbiome (1, 2, 3). Although humans and their pets do not share a genome, they inhabit the same domestic environments, and are exposed to overlapping environmental stressors, including increasingly processed diets, antimicrobial use, and pollutants (3, 4). Close physical contact within shared households also facilitates microbial exchange, resulting in measurable overlap in skin, oral, and environmental microbiota – also referred to as the ‘familiome’ (5). Accumulating evidence suggests that shared environmental exposomes and microbiota contribute to parallel patterns of health and disease across species (6).

The World Health Organization’s One Health framework formally recognizes that human, animal, and environmental health are interdependent and must be addressed as an integrated system rather than in isolation (5). Within this paradigm, domestic dogs and cats increasingly exhibit disease phenotypes that resemble those observed in humans, including atopic dermatitis and obesity (7). These similarities are thought to reflect shared environmental pressures and associated perturbations of the gut and skin microbiota (3).

Direct microbial sharing between pets and owners has been linked to both health and disease. Cohabiting humans and dogs exhibit greater similarity in skin and household microbiota compared with non-cohabiting individuals (3, 8). While such exchanges may enable transmission of pathobionts, including antimicrobial-resistant organisms (9, 10), they may also confer immunological benefits, with early-life exposure to pet-associated microbes in humans associated with enhanced immune maturation and reduced risk of allergic sensitization (11, 12).

Taken together, current evidence supports a bidirectional, microbiome-mediated relationship between pets and their owners, shaped by shared environments. Microbial exchange can support human immune function, particularly in early life; however, pets may also act as reservoirs for pathobionts and antibiotic-resistant bacteria that can transfer to humans. Conversely, human dietary patterns, antimicrobial use, and lifestyle behaviours can disrupt microbial homeostasis in companion animals, contributing to inflammatory and metabolic disease. These reciprocal benefits and risks underscore the need for integrated, ecologically-informed health strategies that recognise pets and owners as a unified biological system.

Future models of pet care may therefore benefit from alignment with One Health principles, incorporating environmental stewardship, microbiome-conscious antimicrobial use, optimized nutrition, and coordinated veterinary–human health strategies. By addressing microbial homeostasis across species, such an approach has the potential to improve disease prevention, enhance immune and metabolic resilience, and redefine companion animal care within a systems-based framework.

4A) Over the next decade, credibility in the pet supplements sector will depend on robust, species-specific clinical evidence, microbiome-conscious formulations, transparent sourcing and alignment with One Health principles.

4B) The most impactful change would be mandatory evidence-based substantiation standards, requiring well-designed, peer-reviewed clinical trials in target species before market approval. Clear labelling of strain specificity, dosage, and safety risk would shift the sector from marketing-driven claims to science-led credibility, strengthening long-term consumer trust.