Roberts, S., Van Loo P., Schultz, P. et al. 2006. Stress and distress: A discussion by the Refinement and Enrichment Forum. Animal Technology and Welfare 5(2), 99-102.

The question was asked: "The terms 'stress' and 'distress' are often used in the scientific literature but usually without a definition. If you use these terms, how do you define them? What are the signs that tell you that an animal is stressed or distressed?" If the subject cannot adapt to the stressor, i.e. return to physiological and behavioural equilibrium, stress becomes distress. Distress is the inability to adapt to a stressor. Distress harms the subject. Pathophysiological processes and maladaptive behaviours typically develop as a result of distress.