Questioner:

Is it permissible to use henna, mixed with egg yolk to condition the hair?

Shaykh ʿAbd al-ʿAzīz ibn Bāz:

There is no problem with that if it involves some benefit. By way of using henna mixed with egg yolk or other natural things. There is no problem with it. If it is good for the hair, such as to make it grow or to make it smooth or other benefits, or and prevent it from falling out, there is no problem with this.