What are the parameters for excusing the touching of impurities during sexual intercourse or foreplay with one's wife, and is sexual intercourse permissible in the presence of impurities?

There is no contradiction between legal opinions permitting the touching of impurity when there is a need, and prohibiting its touching when there is no need. This is because avoiding impurity is commanded. Some scholars, like the Malikis, consider avoiding impurity on the body outside of prayer to be recommended, while the Shafi'is and others believe that becoming smeared with it is not permissible except out of necessity, such as intercourse with someone whose penis has been soiled with madhy (pre-seminal fluid) if water would harm him. Others believe that washing away impurity is obligatory, and that direct contact with it or intercourse while it is present is not permissible except out of dire necessity. As for pure secretions, there is no prohibition in touching them. The more cautious approach is to avoid direct contact with one's wife if impurity is present.