In general, if the hair extensions are made of human hair, you can dye them. You can treat human hair extensions just like you treat the hair on your head. In another word, you can curl, straighten and style your hair extensions. However, if your hair extensions are made of synthetic, you cannot dye them. They could melt, or change completely in texture. If you have synthetic extensions, and you want a different color, you’re going to have to go out and buy more.