Running Irritated Hair Follicles Dying Shampooed Hair?

Dying shampooed hair? - running irritated hair follicles

Mass I permanent hair dyes to dye my roots.
She said that on dry hair without washing them - Do you think it is because the dye does not take too much or because we, the risk of irritation of the scalp to run?
I need a shower and wash hair shop, but want to dye my roots later today.
Good idea or not?