What is the ruling on highlighting the hair?
Question

                What is the ruling on highlighting the hair?.
Praise be to Allah.
    What highlighting the hair means and how it is done is: 

    Some of their hair’s colour is removed, to lighten the 
    original colour of the hair, or to change its colour, or to conceal grey 
    hairs or make the hair shinier. It is done by using a powder that is a 
    mixture of magnesium carbonate and ammonia, to which hydroxide is added. 

    Several methods are used in highlighting the hair, such as 
    rubber caps, foil sheets and rubber cups. 

    Here we will discuss the most well-known method, which is 
    rubber caps, and we will describe this process which is often asked about. 
    Thus the ruling on it will become clear.  

    How highlighting with a cap is done: 

    1.The hair is well combed and 
    combed to the back, taking care to ensure it is dry.

    2.The cap is placed on the head 
    to cover all of the hair.

    3.Hair is pulled out using a 
    special hook, in the direction opposite to that in which it was combed, 
    taking care to keep the locks of hair similar.

    4.The pulled out lock of hair is 
    combed with a fine-tooth comb

    5.The highlighting mixture – 
    which is a powder of magnesium carbonate and ammonia, to which hydroxide is 
    added – is applied to each lock of hair that has been pulled out.

    6.The lock of hair is covered 
    with a thin plastic cover.

    7.The head is exposed to heat to 
    help speed up the lightening process, under constant supervision.

    8.When the desired degree of 
    lightness has been reached, the lock of hair is washed with water.

    9.The resulting colour is left as 
    it is, or another colour may be added to the lock of hair.

    This is the most well-known method. Thus it is clear that 
    highlighting means changing the colour of the hair completely – especially 
    if it is white – and putting another colour, or making the original colour 
    lighter. It is well known that the original colour does not return when this 
    highlighting is done, until the hair grows again. Hence the one who does 
    this process will inevitably lose the original hair colour. 

    These details have been taken from specialized books on 
    cosmetics. 

    Several important points should be noted about highlighting 
    which indicate that it should not be used for other reasons. For example: it 
    is not permissible to dye hair black for one whose hair has turned grey, or 
    to resemble kaafir women or immoral women; it is not permissible for a woman 
    to show her hair to non-mahram men; and no harm should be caused to the head 
    by using these chemical substances for highlighting. 

    If highlighting is free of these concerns, then there is 
    nothing wrong with using it. 

    See also questions no.
    45191 and
    6455 for information on the 
    ruling on dyeing hair black and imitating immoral women and kaafir women 
    when dyeing the hair. 

    And Allaah knows best.