Reverting to Chemical Hair Dyes after Henna
If henna isn’t for you and you want to get back to commercial hair dyes, it’s fine to backtrack within 2 - 3 weeks and it shouldn’t be a problem, but ideally I would say you should wait a couple of months or longer after your last henna application; if that’s too long then try, if you can, to aim for at least one month. If you’re not keen on henna, for whatever reason, the sooner you decide the better. The longer you leave it and the more you use henna, the more the henna colour will build up in your hair and the harder it may be to get good colour take with your commercial hair dye. How long henna lasts varies considerably from person to person. Henna has the potential to be a permanent hair colour, especially on grey hair. Mine lasts for ages and never seems to completely disappear even when I haven’t used henna for months. Over time henna will fade and in theory - at least in the early days of your first & second time use of henna - it should slowly ( but not necessarily) wash out. If you’ve used henna more than once or twice, chances are it may literally have to grow out.
If you’re desperate to tone down a henna hair colour, try washing your hair with yoghurt, and basically wash your hair as much as possible with a good detergent based shampoo (take your pick - the commercial market is full of them); and don’t use hair conditioner. After washing the living daylights out of your hair, you’ll need some cassia obovata to restore your hair to its shining glory. Cassia obovata is the best hair conditioner for damaged hair.
I would say that if you want to go back to chemical dyes, try to wait at least a couple of months if you can, but if you simply can’t stand the wait then strand test with your normal hair dye before applying it to the entire hair to see how it takes. The worst that’s likely to happen if you use the hair dye too soon is that you’ll have wasted a pack of hair dye if the colour doesn’t take. I can’t tell you exactly when your hair will be ready to take commercial hair dye colour again, but it’s likely that within 2 - 3 weeks of your last henna hair dye application you will manage a good colour take. Remember that henna’s natural function is to act as a barrier to things which are harmful to your hair and, if we’re thinking straight, I think you’ll agree that every credit goes to natural henna for trying its utmost to keep what’s bad from entering your hair.