What radiation dose is associated with the onset of erythema?

The onset of erythema, which is a reddening of the skin due to radiation exposure, typically occurs at a dose of around 200 rad (or 2 Gy) in adult humans. This dose is significant enough to cause acute skin reactions, including erythema, as it directly affects the mitotic activity of skin cells and can lead to changes in the vascular response of the skin.

At doses lower than this threshold, such as 50 rad and 100 rad, the body can generally handle radiation without significant immediate skin effects. It isn’t until the dose reaches approximately 200 rad that the biological response becomes pronounced enough to result in visible symptoms like erythema. A dose above this level increases the likelihood of more severe effects, but 200 rad is recognized as the approximate baseline for observable skin changes in response to radiation exposure.