1. Is the sewan (dried oil) that comes out of the body impure? 2. What is the amount of impurity that necessitates ghusl for prayer? 3. What should I do when I suspect I have been afflicted by an impurity from the street, and it is difficult for me to investigate?

Pus resulting from pustules, sores, or a wound is considered impure (najis). However, if it is merely oiliness or slight moisture emanating from skin pores, and not from pustules, sores, or a wound, then it is not impure. Whoever doubts that they have been afflicted by impurity should sprinkle water (nadh) on the doubtful area according to the Malikis. As for the Shafi'is, nothing is incumbent upon them as long as they are in doubt, except that the Malikis made an exception for impurities on the road, in which case sprinkling is not obligatory if one doubts or has a weak presumption about it, provided its substance is not visible. However, if one doubts the impurity of something that has afflicted them, nothing is obligatory upon them.