A common perspective on stress-related changes in the human immune system is that such changes are potentially harmful, especially those occurring during chronic stress. In contrast, an ecological perspective views the immune system as an energetically costly system that may or may not have priority over other uses of that energy. From this perspective, the immune system may have energy made available for it via reduction of other activities, may change in energetically conservative ways when the protection it confers needs to be balanced with the energetic demands of other activities such as fight or flight, or may be suppressed when other activities are more important than immunity for total well-being. This last type of change can explain why aspects of psychosocial health such as optimism relate to worse immunity under some circumstances and suggests that both benefits and costs of immunosuppression during stress should be considered in research on human stress and immunity.