How Hair Dyes Work
Way back in the days when hair dyeing was still in its infancy, hair dye color products routinely gave off a quite disgusting rotten egg type of smell. It is good news then that today, the modern equivalents of these old fashioned products have a much nicer smell. The great thing about these present versions is that they are much simpler to apply as well. It doesn’t matter if it’s to wet hair or dry, quite a few of the colouring products available today can be massaged into the scalp forming a shampoo like lather, left to work its magic (with or without a plastic hair covering piece, depending on the product) then rinsed out and conditioned. How simple is that?
Unfortunately, simplicity comes at a price, as is most often the case in life. Chemicals present in the hair dye, such as ammonia and peroxide, can be just as harsh and damaging to your hair today as were the chemicals in the early days of hair colouring, and this is especially true if you dye your hair too often. Obviously your hair is going to react differently to different levels of the chemicals found in various types of products, but generally there are three main types of hair colouring levels used by the main hair product companies today- semi-permanent, demi-permanent and permanent.
Semi-permanent colour basically adds colour to the hair without changing the natural colouring too much. This kind of hair dye consists of tiny molecules that enter the hair through the cuticle but do not affect the hairs natural pigmentation. After several washes these molecules, because they are so small, eventually exit the hair shaft leaving your hair as it was before the hair dyeing treatment. Semi-permanent hair dye usually lasts from six to twelve shampoos and has the ability to cover up to fifty percent of your greys. It enhances the natural colouring of your hair but doesn’t lighten it due to the fact that it contains no ammonia or peroxide.
Demi-permanent hair dye colours usually last a lot longer than the semi-permanent variety, at around 22-28 shampoos. The pre-coloured molecules enter the hair through the cuticle, as in the semi-permanent dye but once in the hairs cortex they fuse with other molecules to give medium sized colour molecules. Because these molecules are larger in size, they now take that much longer to wash out of the hair. Demi-permanent hair dye does not contain any ammonia so the natural pigmentation of the hair cannot be lightened, but it does contain a small amount of peroxide which allows for slight (but noticeable) colour change.
Permanent hair dye is what is used for major hair colour changes, for example going from black to blonde or vice-versa. Permanent hair dye uses both peroxide and ammonia so when the molecules enter the hair they react and expand to a size that cannot actually be washed out. The only way out with this method, apart from re-dyeing, is to let the hair grow out. This type of hair dye reacts by lightening your natural hair pigmentation, forming a new base and then adding a new permanent colour which combines with your own natural hair pigment. This is the reason the colour you have to chosen to dye your hair with may look different on you than on someone else who has used the same colour. As hair grows at a rate of about half an inch a month, this kind of hair dye will present the problem of roots, so you will probably need to touch up the dye every few weeks.
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