Preventive interventions can potentially produce great harms to the individual health. Quaternary prevention (P4) is a balanced initiative to avoid unnecessary medicalization and iatrogenesis, such as overdiagnosis and overtreatment 1. P4 is defined as an action taken to identify people at risk of overmedicalization, to protect them from the excesses of biomedical interventions, and to offer ethically acceptable alternatives 2. This article discusses the Precautionary Principle (PP) to strengthen P4 when dealing with additive preventive measures such as breast cancer screening. According to Geoffrey Rose 3 , additive preventive measures are generally professional-led interventions that are alien to human ecology, economy, and physiology. These include drugs, vaccines and other biological, physical, and chemical products. Additive preventive measures can produce harm without potential benefit since most individuals are asymptomatic (healthy) and not destined to become sick in the future. Consequently, additive preventive measures cannot be considered safe and policymakers are accountable for providing evidence of their net benefit. This context is different from reductive preventive measures. Rose 3 (p. 94) defines reductive preventive measures as "removing or reducing some unnatural exposure in order to restore a state of biological normality". The aim of reductive preventive measures is to diminish artificial exposures to the individual and population health. This implies changes in ways of living that are known to be pathogenic or to carry greater health risk. By restoring biological normality to the individuals-defined as "conditions to which we are thought to be genetically adapted through our evolutionary history" 3 (p. 94)-, reductive preventive measures can enhance individual health. In clinical settings, it refers to guidance and counselling to reduce sedentary behaviour, smoking, obesity, etc. In public health and social organization, it focusses on reducing economic, social disparities 4 , and promoting other health activities. Reductive preventive measures are safe, having no or minimal potential harm to people's health. The distinction between additive and reductive preventive measures is a watershed within the universe of prevention. It offers an operational framework that facilitates the implementations of reductive preventive initiatives, while simultaneously increases the safety thresholds upon additive preventive measures. The safety, technical, and bioethical requirements to approve an additive preventive measure are greater due to their embedded potential harms. As Rose 3 (p. 94) remarks, "there can be no prior presupposition of safety, and hence the required evidence of benefit and (particularly) safety must be more stringent".