What is the ruling on fashion design in Islam, and what are the permissible and forbidden aspects of this profession?

The criterion for the permissibility of an action is that it should not lead to something forbidden or include it. If fashion designs are modest, do not resemble those of disbelieving and immoral women, and are used for adornment before husbands, with the assurance that they will not be displayed before non-mahram men, then they are permissible. However, if they are used for ostentatious display (tabarruj) and worn in the streets, then they are forbidden, because they contribute to sin.