It’s a very good question because the nature of your real hair and that of the extensions is different. For extensions, there can be natural, albeit dead, hair and synthetic hair.
First and foremost, we’d advise to choose the right hair colour for the extensions straight away. Your favourite stylist can help you choose the colour that is closest to the shade of your current hair.
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Colouring Synthetic Hair Extensions Won't Work
Colouring won’t work on synthetic hair. Or rather, regular hair dyes won’t work as synthetic hair lacks the natural pigment contained in human hair. There are ways to colour synthetic hair but we won’t delve into this.
Dying Human Hair Extensions Is Possible But Not Advised
It’s possible to colour to colour human hair extensions, although it’s trickier than colouring your natural hair. Under normal circumstances, several factors can influence the final result of a colouring: the state of the hair (damaged, porous), its capacity to absorb the colour, the difference in colour between the root and the tip, etc. Most hair extensions are coloured and go through a pretty aggressive processing. As a result, their cuticle layer is usually damaged.
Bear in mind that not all hair extensions are equal, and always research the provider before you buy any hair extensions. High-end extensions are pricier but last longer, which, in most cases, makes them better value for money over time.
Maintenance is also an important factor to keep in mind to make the most out of your extensions, whether they're dyied or not. Make sure that you have the right tools and an appropriate routine.
Dying Your Humain Hair Extensions Darker
For the reasons stated above, as a general rule, we woudn't advise colouring hair extensions. Dying them a shade or two darker isn’t’ usually an issue but we don’t recommend going any further than that, otherwise the hair may get ever more damaged with an unpredictable outcome. That's why it's important to seek help from a professionally trained hairdresser, to ensure that you pick the right hair extensions shade in the first place. We can help with that ;).
Bleaching Humain Hair Extensions
We’d strongly advise against bleaching hair extensions, whether they’re natural or synthetic. Bleaching synthetic extensions will do nothing but burn them (plastic!). As explained above, as almost all natural hair extensions are processed and coloured, they're more fragile than your natural hair. Bleaching them is likely to cause further damage, and one of these 2 outcomes is likely to happen:
You won’t get the results you wanted
The extensions are so damaged that they end up in the bin
In any case, don’t lighten your natural hair extensions by more than one or two shades.
Colouring your extensions should ideally be done before they’re fitted as it’s a lot easier. The result is likely to be better and it will save you money.