Can something forbidden become permissible due to necessity, and what are the conditions for that?

Permitting the forbidden due to need (hajah) is correct. It differs from necessity (darurah) in that hajah is a hardship that afflicts a person by abandoning something, whereas darurah is harm that afflicts him due to the absence of something. A condition for permitting the forbidden due to hajah is that the forbidden act must be prohibited as a means, not as an end, such as eating carrion and drinking intoxicants. Examples of what is permitted due to hajah include a man wearing silk for itching, and permitting riba al-fadl (usury of surplus) in 'araya (selling fresh dates for dried dates by measure). Sheikh Al-Uthaymeen pointed to this, saying: "But what is forbidden as a preventative measure… is permissible due to hajah, like the 'ariyya." Similarly, looking at the face of a non-mahram woman is forbidden because it is a means to indecency, but it is permissible due to hajah, such as for marriage proposal or testimony, because its prohibition is a prohibition of a means.