Depending on their duration and depth (penetration), hair dye cosmetics can be classified as bleaches, permanent dyes, semi-permanent dyes and temporary dyes. It is not expected that the hair will be damaged by these products in a one-time application; However, it can damage the hair due to the application of dyes many times and the treatment with heavy chemicals. The most damaging process to hair is bleaching. There are 2 types of bleach: First, those containing oxygenated water (hydrogen peroxide), which are used more often, and secondly, those containing zinc formaldehyde sulfoxylate. In bleaches containing hydrogen peroxide, at high PH (10) degrees, the active agent reacts with the melanin pigment in the cortex of the hair and turns the hair into a lighter color. Bleaches are products that are well tolerated when used appropriately. However, at intervals of 6-8 weeks or more frequently, it can cause protein loss due to damage to the hair tip, contact dermatitis and allergy on the skin.
Permanent hair dyes are the most preferred products in the market. Hair dyes contain about 3-6% hydrogen peroxide and dyestuff (p-Phenylenediamine/PPD or aminophenols) at varying rates. The PH must be high (around 10) so that the dye can enter the hair shaft, the cortex; for this, ammonium or ethanolamines are used in paint products. Hydrogen peroxide both oxidizes melanin, in the hair shaft, and pairs with dye precursor molecules to form new colored molecules in the hair cortex. After applying permanent hair dyes, the hair color cannot be easily removed with shampoo, it is resistant to high heat and light. Hair damage from the use of these products is not actually due to the dye itself. It is mostly due to the fact that the alkali components in its content cause swelling in the hair fiber and damage the outer shell (cuticle) of the hair and protein loss. In order to minimize the damage, it is recommended that the permanent dye used should not be much lighter or darker than the original hair, and it should be as close to the original color of the hair as possible.
Since semi-permanent dyes do not contain amonium and ethanolamine but contain hydrogen peroxide (2%) at a lower concentration, of course, they cause less damage to the hair compared to permanent dyes. The hydrogen peroxide content in hair dyes is very critical. As the hydrogen peroxide content decreases, the rate of penetration of the product into the hair fiber decreases and the dye is removed from the hair faster. For example, semi-permanent hair dyes containing 2% hydrogen peroxide are durable up to 12-14 washes; When the amount of hydrogen peroxide decreases, this number decreases to 6-10 washes and hair dyes that do not contain any hydrogen peroxide are temporary dyes and the dye can be removed from the hair in 1-2 washes. Temporary dyes are mostly used to reduce graying in original hair, cover graying, and reduce unwanted tones. These temporary dyes are commercially available in the form of shampoo or cream and are used on wet, newly shampooed hair and then rinsed off.
Permanent dyes increase the water permeability of the hair by damaging the outer structure of the hair fiber, the cuticle layer, causing a high degree of protein loss and destructive damage.
The hydrogen peroxide ratio in permanent hair dyes is between 3% and 6%. To reduce hair damage, semi-permanent hair dyes containing 2% hydrogen peroxide should be used and bleaches that damage hair proteins should be avoided.