Having proved flaws in using clinical trials to study weak factors, we want to investigate how life factors affect health and diseases. In this study, we show that cancer, heart disease and infectious diseases are inherently preventable and curable. We would like to find how life factors revolving around environment, emotion, activity, disease agents, diets, behaviors, etc. affect disease outcomes. We expand the scope of the immune functions to include functions for removing garbage and repairing tissue damages, and then identify six classes of health properties for evaluating the immune system’s actual functional capabilities. In this model, personal ability to resist infection depends on the immune system’s current functional capabilities, and the ability to resolve existing diseases depends on the immune system’s actual functional capabilities integrated over a relevant time. We show how each life factor affects the immune system’s current functional capabilities by examining its effects on any of the six classes of properties. Many seemingly irrelevant factors can affect disease outcomes because they share biological resources for removing garbage, repairing tissue damages and maintaining all vital functions. Thus, we found that rational strategies for conquering diseases are identifying disease causes, avoiding exposure to disease agents, detoxifying toxic substances, and using seemingly-irrelevant life factors to boost real-time immune functional capabilities and vital organ functions. All chronic diseases including personal resistance to SARS-CoV-2 are influenced by N and M factors, where N represents the number of factors related to disease causes, and M represents the number of factors that influence the immune functional capacities and organ capacities. Most of N factors are pollutants while most of M factors are created social practices that are formed after industrial revolution. It is time to address toxic substances and examine health-ruining social practices in education, employment, business, litigation, promotion, etc. which is responsible for switching on human stress hormones for months and years, with predictable adverse effects on human health.