This paper examines the prevention of the exponential growth of aflatoxin occurring in multi-month, postharvest storage in tropical countries, with examples from field experience and scientific data. Four approaches to modern, safe, postharvest storage methods are described, the most successful being the use of flexible, UltraHermetic™ airtight structures that create an unbreatheable atmosphere (low oxygen, high carbon dioxide) through insect and microorganism respiration alone, without use of chemicals, fumigants, vacuum, or refrigeration.The increase in aflatoxin levels during multi-month, postharvest storage is a serious health hazard affecting several major crops. During postharvest crop storage by conventional methods in tropical conditions, molds existing within crops can produce aflatoxin levels many times greater than at harvest, often vastly exceeding the international safety standards of 20 ppb (parts per billion). For example, field data from Mali documents that during just two months of conventional peanut storage, average aflatoxin levels rose 200%. In Uganda, aflatoxin levels in conventionally stored maize rose 300% in three months. By contrast, laboratory and field data from Mali and Uganda show that the organically modified atmosphere created using various forms of sufficiently hermetic (airtight) storage containers (ranging from 25kg to 1000-tonne capacity) prevents the exponential growth of aflatoxin-producing molds in various grains, peanuts, and seeds.