The medical effects of a nuclear blast upon humans can be put into four categories:

Initial stage -- the first 1–2 weeks, in which are the greatest number of deaths, with 90% due to thermal injury and/or blast effects and 10% due to super-lethal radiation exposure



Intermediate stage -- from 3–8 weeks. The deaths in this period are from ionization radiation in the median lethal range


Late period -- lasting from 8–20 weeks. This period has some improvement in survivors' condition.




Delayed period -- from 20+ weeks. Characterized by “numerous complications, mostly related to healing of thermal and mechanical injuries coupled with infertility, sub-fertility and blood disorders caused by radiation.” Also, ionizing radiation from fallout can cause genetic effects, birth defects, cancer, cataracts and other effects in organs and tissue.