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Demi-permanent hair dye is a chemical agent used to color hair. Unlike longer-lasting versions, it has no ammonia and a very low peroxide content. The color molecules are not as large, as well, so they wash out in about 24 shampoos. It has advantages such as being compatible with previously treated strands, but it also may pose serious health risks and has some drawbacks such as being ineffective at lightening color.
How It Works
The different types of hair color are separated by two major factors: whether they react with the natural pigment, and what size the color molecules are. In a temporary types, the molecules are very small. Ammonia, which is the agent that lifts the outer cuticle layer of the strand so dye can get inside to the deeper inner cortex, is not present. This, combined with very low peroxide levels, means the dye doesn’t lighten the natural pigments. It merely coats the strands with deposits of additional color molecules.
Permanent formulas contain ammonia, so they are able to lift the cuticle. They also have peroxide, which helps strip some or all of the natural pigment from the cortex. Color molecules enter the stripped strands, which creates a blend of the person’s natural color and the dye color. The molecules in this type of product are too large to get washed out easily.
A demi-permanent hair dye falls in between temporary and permanent. It uses an ammonia subtitute and has a very low peroxide percentage, so it doesn’t react with natural pigments and can only add color. The pre-color molecules in the product start out small but then join together once they’ve gotten into the cortex. The larger molecules are big enough that they can’t come right out but are small enough that they don’t have the staying power found in a long-lasting formula.
Purpose and Use
Based on the chemical makeup of demi-permanent hair dye and how it works, when a person has already used a coloring agent, this type of color can refresh the existing hue with very little additional damage. The cosmetologist uses a permanent formula only on new growth. An individual who doesn’t want to commit to a shade but who wants her color boost to last longer than it would using a temporary option also may use this type of product. Many people use it to blend away gray.
Due to the use of an ammonia substitute and low level of peroxide, demi-permanent hair dye is fairly gentle. Many versions can be used on newly-relaxed or permed tresses without the risk of further chemical damage. They can give a bit of texture or add shine. In fact, some versions that are meant solely for these latter purposes are colorless. These products also permit people to experiment with color changes and are a good choice for individuals who want to color at home.
Dyes that fall into the demi-permanent category are not good at lightening hair, even by a shade or two. They still take time to apply. The fact they wash out in around 24 shampoos means that a person usually needs to use them more often than with a longer-lasting option. If the work is done at a salon, this can get expensive.
Some health professionals are concerned about the potential health risks demi-permanent and other dyes have as a result of their chemical ingredients. These agents can cause skin irritation on some people and have been found to cause cancer in lab animals. Experts are studying whether the chemicals can cause potential problems during pregnancy, because mothers-to-be can absorb them through the skin in very small amounts. The American Pregnancy Association recommends avoiding coloring products at least during the first trimester, as not enough research has been done to determine exactly how big the risks of pregnancy complications or birth defects are.
Virtually all licensed salons offer coloring services that use these products. At-home kits are available in the hair care aisles of most department stores, as well. People routinely buy this variety of hair color online if their local stores don’t have the brand or exact shade they want.