Every time I dye my hair, with permanent dye, it washes out in 5 washes. What can I do to keep the dye in?

How do I get my hair dye to stay?

Interestingly, demi-permanents are often more permanent on porous hair than "permanent" dyes. It has to do with the size of the molecules and the ability of the molecules to get into the hair. On virgin hair, demi-permanet molecules are too big to get inside. Therefore, it will wash out after 20 shampoos (roughly). On the other hand, if the hair is very porous, the demi-s actually get inside the cuticle and, since they're larger than the "permanent" molecules, it's harder for them to wash out. Fading is, therfore, reduced.