* Underlying Pigment Exposure: Hair contains natural pigments called melanin, which come in two main types:
* Eumelanin: Produces brown and black tones.
* Pheomelanin: Produces red and yellow tones.
When you bleach hair, the process breaks down these melanin molecules. Eumelanin is generally easier to break down than pheomelanin. So, as you bleach, the darker pigments (brown/black) are often lifted first, revealing the underlying red and yellow pigments from the pheomelanin. If the bleaching process isn't taken far enough, or if the hair is naturally rich in red/yellow pigments, the remaining dominant color will be orange or brassy.
* Incomplete Bleaching: Achieving a true blonde shade requires lifting the hair past the orange/yellow stages. If the bleach isn't strong enough, doesn't process for long enough, or isn't applied evenly, it may only remove some of the pigment, leaving the remaining orange tones visible.
* Hair's Natural Undertones: Some hair naturally has stronger red or orange undertones than others. This means that even with bleaching, it can be more challenging to completely remove these warm tones and achieve a cool, neutral blonde.
* Damage and Porosity: Damaged hair can be more porous. Porous hair loses color faster, and can be more prone to absorbing minerals and impurities from water (like iron), which can also contribute to brassiness and orange tones.
In summary, blonde hair turns orange after bleaching because the bleach lifts the darker pigments first, leaving the underlying red and yellow pigments exposed, or because the bleaching process wasn't sufficient to remove all the warm tones from the hair.
To avoid this, professional colorists use a combination of strong bleaching agents, careful timing, and toner to neutralize unwanted warm tones and achieve the desired blonde shade. At home, you can use blue or purple shampoos to neutralize unwanted warm tones.