How can all animal hair and human hair be pure, while some say that the product L-cysteine is impure, and it is impermissible to consume foods containing it, given that it is made from animal hair, human hair, or synthetically? And is it permissible to eat pasta that contains chicken powder, along with the permissibility of eating meat from the lands of the People of the Book?

Human hair is pure, whether the person is alive or dead. It is not permissible to benefit from it through sale or use, due to the dignity of the human being. As for animal hair, there is a detailed explanation: The hair of an animal whose meat is permissible to eat is pure, whether it is attached or detached. The hair of an animal whose meat is not permissible to eat, while it is attached to it, is pure, except for pigs and dogs according to some madhhabs. As for the hair of an animal whose meat is not permissible to eat, once it is detached, there is a difference of opinion: Hanafis and Malikis consider it pure, while Shafi'is consider it impure. As for the hair of a dead animal, Hanafis, Malikis, and Hanbalis hold that it is pure if the animal was pure during its lifetime, whereas Shafi'is consider it impure. According to the majority, a pig is impure during its lifetime, so its dead hair is impure, except for the Malikis.

If hair is processed and undergoes a transformation from its original state, it is permissible to consume it if it is free from harm. Chicken powder, if it comes from ritually slaughtered chicken, is permissible (halal). If it comes from chicken not ritually slaughtered according to Islamic law, then it is impure (najis) and forbidden (haram).