When it is permissible to use cosmetics? And the ruling on collagen in particular
In principle it is permissible for women to use cosmetics, but when saying it is permissible it is essential to pay attention to a number of things, such as:
This beautification should not be for non-mahram men. The one for whom she should beautify herself first and foremost is her husband. If she uses cosmetics so that her husband will see her in the best shape, or she appears thus beautified before other women or her mahrams, that is permissible for her, because the basic principle is that she should cover all of her body in front of non-mahram men, so how can it be permissible for her to beautify herself for them in addition to that?
The materials used for cosmetic purposes should be permissible, such as henna and kohl. It is not permissible for her to use fat from dead meat (i.e., from animals that have not been slaughtered in accordance with sharee’ah) or impure (naajis) substances, because Islam forbids using impure and haraam things. See the answer to question no. 45635.
The materials used for cosmetic purposes should not be harmful to her body. It is not permissible for her to use harmful chemical substances, whether the harmful effect will occur immediately or in the future, because Islam forbids harming oneself, as the Prophet (peace and blessings of Allaah be upon him) said: “There should be neither causing harm nor reciprocating harm.”
The cosmetic effect on the body should be temporary. It is not permissible for her to use those substances that change the creation of Allaah, as some women do by having lip treatments, face peeling and tattoos which change the colour of the skin permanently.
In the answer to question 34215 we have stated that face peeling is haraam, and that it is changing the creation of Allaah.
In the answer to question no. 47694 we discussed the ruling on cosmetic surgery, and we stated that some of it may be essential, so it is permissible, and some of it is merely for the purpose of beautification, and it is haraam, because it comes under the heading of changing the creation of Allaah. One of the examples we mentioned was face lifts.
If the conditions and guidelines mentioned above are met, then using collagen is permissible.
And Allaah knows best.