Hydrogen peroxide is the primary ingredient that enables permanent color change in hair products, often found in concentrations ranging from 3% to 12%. While necessary for permanent hair coloring, it is incorporated as a measured component in a developer solution, rather than being used as a standalone “dye.” Using peroxide by itself primarily results in the removal of natural pigment, a process known as lightening, which is chemically distinct from true dyeing that deposits a new color.
The Chemical Action of Peroxide on Hair
The fundamental action of hydrogen peroxide on hair is oxidation, facilitated by an alkaline agent like ammonia in commercial hair color products. This alkaline environment causes the protective outer layer of the hair shaft, the cuticle, to swell and lift. The lifted cuticle allows peroxide molecules to penetrate the hair’s inner structure, the cortex, where the natural color pigment, melanin, is stored.
Once inside the cortex, the peroxide oxidizes the melanin, breaking down the large pigment molecules into smaller, colorless compounds. This decomposition lightens the hair, providing a blank canvas for new color. The oxidative process also causes untargeted chemical changes, including the oxidation of structural proteins in the hair’s keratin.
Peroxide Used Alone: Lightening, Not Dyeing
Applying household-strength hydrogen peroxide (typically 3%) directly to the hair is a common attempt to achieve a lighter shade. This method is a form of bleaching because it only removes existing color pigment without depositing new dye molecules. The outcome of this solo application is often unpredictable, especially for individuals with darker hair. When natural pigment breaks down, it lightens in stages, moving through red and orange undertones before reaching yellow. Without the counter-pigments found in professional dye formulas, the solo use of peroxide frequently results in an undesirable orange or brassy yellow tone.
The application is also difficult to control, often resulting in an uneven or patchy color outcome. Applying peroxide directly strips the hair of its natural protective oils, leading to immediate structural damage and a negative change in texture. This damage is permanent; while conditioning can temporarily counteract the dryness, the hair structure remains compromised.
Peroxide’s Essential Role in Commercial Dye Kits
Hydrogen peroxide is intended for use as the primary component in a hair color developer, where it activates the dye. The developer solution is mixed with the colorant tube, which contains dye precursors and coupling agents. The developer has a two-fold function: it prepares the hair by lifting the cuticle and breaking down some natural melanin, and it initiates the oxidation and coupling reaction of the dye molecules.
The strength of the developer is measured in “volume,” with common volumes being 10, 20, 30, and 40, corresponding to approximate hydrogen peroxide concentrations of 3%, 6%, 9%, and 12%. A 10 volume developer is used primarily for depositing color or toning without significant lightening. A 20 volume is the most common, offering 1 to 2 levels of lift and full gray coverage. Higher volumes (30 and 40) are reserved for substantial lightening, such as achieving several levels of lift on dark hair.
Safety Measures and Minimizing Hair Damage
Since the oxidative process damages the hair’s protein structure, several steps should be taken to mitigate harm and ensure a safe coloring experience. The first step is the patch test, which involves applying a small amount of the mixed product to a discreet area of skin (such as behind the ear or inner elbow) and leaving it for 48 hours to check for allergic reactions. This precaution must be performed before every coloring session.
A strand test is also recommended to determine the expected color result and the hair’s tolerance before full application. This involves applying the mixed product to a small, hidden section of hair and observing the outcome after the recommended processing time. To minimize chemical damage, the lowest effective developer volume should be chosen, and the processing time must be limited strictly to the manufacturer’s instructions. Post-coloring care should focus on replenishing moisture and protein lost during oxidation, using deep conditioning treatments, and avoiding excessive heat styling.