Because synthetic hair extensions are made of plastic, you cannot dye them. However, anything that you can do to your natural hair, you can do to human hair extensions. If you have black human hair extensions that you want to dye, you must follow the same process that you would to dye your own hair. Just as with human hair, start with a strand test before dying the entire hairpiece to make sure that the end result is the outcome that you desire.
Apply a deep conditioner to the hair. Use a deep conditioning cream to moisturise the hair and let it sit for 10 minutes. Rinse and dry the hair thoroughly to prepare it for colour stripping.
Lighten the hair with bleach. Hair bleach will strip the black colour from your hair extensions, turning the hair into a light-orange colour. Because the hair is black, you may need a second application of bleach to make the extensions light blonde. Condition the hair again after removing the bleach and allow it to dry thoroughly.
Dye the hair extensions to your desired colour. Enhance the blonde colour by adding blond dye, or change the hair colour entirely. Condition the hair extensions again after rinsing the dye out and regularly apply a leave-in conditioner to keep the hair looking natural.
Colouring hair extensions require you to use strong, professional-strength chemicals, and misusing these chemicals can damage your extensions beyond repair. Let a professional dye your hair extensions if you have no experience with bleaching or colouring hair. Chemicals that are too strong damage the hair cuticle and leave the hair dry and brittle. Regardless of your experience level, hire a professional to dye hair if you are not sure what strength chemicals your extensions require.