The article explores the relationship between oxidative stress, immune and detoxification systems, and condition-dependent sexual signals in animals. It suggests that oxidative stress, generated by immune and detoxification processes, influences the expression of sexual ornaments, which in turn can signal an individual's genetic quality. Female choice for mates with exaggerated ornaments may thus promote the evolution of these traits, as they reflect the bearer's ability to withstand oxidative stress. The immune and detoxification systems are highly polymorphic, contributing to individual differences in health and survival. Genes involved in these systems, such as those in the major histocompatibility complex (MHC) and cytochrome P450 (CYP) families, show significant allelic variation, which may affect an individual's resistance to pathogens and toxins. Oxidative stress is a major contributor to aging and various diseases, and its levels are influenced by the efficiency of antioxidant defenses. The condition-dependent expression of sexual ornaments, such as carotenoid pigmentation, song repertoire, and comb size, is sensitive to oxidative stress, making them reliable indicators of an individual's health and genetic quality. The study highlights the importance of understanding the physiological mechanisms linking oxidative stress to sexual signals and the role of genetic variation in these systems in evolutionary processes.The article explores the relationship between oxidative stress, immune and detoxification systems, and condition-dependent sexual signals in animals. It suggests that oxidative stress, generated by immune and detoxification processes, influences the expression of sexual ornaments, which in turn can signal an individual's genetic quality. Female choice for mates with exaggerated ornaments may thus promote the evolution of these traits, as they reflect the bearer's ability to withstand oxidative stress. The immune and detoxification systems are highly polymorphic, contributing to individual differences in health and survival. Genes involved in these systems, such as those in the major histocompatibility complex (MHC) and cytochrome P450 (CYP) families, show significant allelic variation, which may affect an individual's resistance to pathogens and toxins. Oxidative stress is a major contributor to aging and various diseases, and its levels are influenced by the efficiency of antioxidant defenses. The condition-dependent expression of sexual ornaments, such as carotenoid pigmentation, song repertoire, and comb size, is sensitive to oxidative stress, making them reliable indicators of an individual's health and genetic quality. The study highlights the importance of understanding the physiological mechanisms linking oxidative stress to sexual signals and the role of genetic variation in these systems in evolutionary processes.