Abstract <p>Hair is a noninvasive biomatrix that can provide information on the activation of the hypothalamic–pituitary–adrenal axis, the maintenance of homeostasis, and the success of an animal’s adaptation to natural and anthropogenic stressors. The literature studying the relationship between the hair cortisol concentration detected in farm, domestic, and wild animals with various biological parameters and behavioral factors is reviewed. It is noted that the hair cortisol concentration mainly correlates with the animal species, sex, age, sampling location, color, pregnancy, season of the year, housing conditions, the presence of diseases, and behavioral characteristics. Some factors can be directly related to stress and animal adaptation to changing conditions, which is reflected in the blood cortisol concentration and its subsequent release into the hair shaft, or be inconsistent and species dependent.</p>