In my previous article, we’ve looked at two types of hair dyes: temporary and semi-permanent hair dyes, both of which are non-oxidative. Two other commonly used types of hair dyes are the demi-permanent and permanent hair dyes, both of which fall into the oxidative category. In this article let’s take a look at the demi-permanent hair dyes.
What does ‘oxidative’ refer to?
In oxidiative hair coloring, the dyes are only formed once the dye precursors (small colorless molecules) have penetrated the hair fiber, and require both hydrogen peroxide and a base such as ammonia or monoethanol amine (MEA) for successful deposition.
Demi-permanent oxidative hair dyes
Demi-permanent hair dyes are an intermediate between the semi-permanent dyes and permanent hair dyes. Demi-permanent hair products promote major hair color durability (resistance up to 20 washes) because they consist of a mix of semi-permanent molecules as well oxidation dye precursors. They are usually applied in the presence of hydrogen peroxide and a base such as MEA.
The combined effects of having some big dye molecules formed inside the hair and the smaller pre-formed dye molecules (from the semi-permanent category) that can attach to the hair surface/ diffuse inside the hair, are what make the demi-permanent dyes more durable. Additionally, they allow more versatility in shade development as compared to demi-permanent hair dyes alone. Bear in mind that while the color stays in the hair for up to around 20 washes, it does not imply that that the color stays fresh and vibrant for that long. Most people recolor way before 20 washes as the shades fade or shift color through the shampoo cycles.
Because the cuticles are opened and eventually closed during the dying process, and the hydrogen peroxide modifies the melanin of the hair to some extent, the hair experiences more internal damage than if it were dyed with semi-permanent only. However, many people choose this option because:
- It has several nice shades
- It is good enough to touch up on grey (~ 50% coverage)
- It does not cause too much damage
- It is a good transition to permanent hair dyes. In case of accidents, the colors are easier to correct.
Find out more about permanent hair dyes here.