Stress in Indoor and Outdoor Cats: Association between Hair Cortisol Levels, Housing Style, and Guardians’ Perceptions of Behavior

This study evaluated hair cortisol as a biomarker of chronic stress in 34 domestic cats (<i>Felis catus</i>), comparing indoor and outdoor individuals. The aim was to investigate associations between hormonal levels, physical and social environmental characteristics, and behavioral indicators related to feline welfare. Hair samples were analyzed using the ELISA method, and guardians completed structured questionnaires. The overall mean cortisol concentration was 2.52 pg/mg, with no significant difference between indoor (2.40 pg/mg) and outdoor (2.62 pg/mg; <i>p</i> = 0.510) groups, suggesting that both housing styles may be compatible with low physiological stress levels. Indoor cats were associated with more intentionally enriched environments, including litter boxes, hiding places, vertical spaces, and predatory stimuli, highlighting the importance of resources provided by the owners indoors. Cats exhibiting behaviors such as isolation and excessive vocalization showed higher cortisol levels, while perceived stress reported by guardians did not correlate with hormonal data. The findings reinforce the relevance of environmental enrichment for feline welfare. Studies with larger samples are recommended to deepen these associations and support the dissemination of effective environmental management practices for domestic cats.