Ionizing radiation refers to the flow of material particles or photons of electromagnetic radiation that can ionize atoms of the environment through which it passes. At the cellular level, damage can be manifested by cell death or changing their cytogenetic information. These events can lead to adverse tissue reactions (deterministic effects) in which manifestations depend on exceeding the dose threshold, or to the stochastic effects, when the probability of damage increases with the dose. This article briefly summarizes these effects on the human body.