How can one differentiate between obsessive doubt (waswas) and a normal matter related to impurity (najāsa)? Is something considered pure if its impurity was certain, and then you touched it and subsequently touched other things with it without seeing the impurity on them? Is a sticky substance, like something wet, considered to become impure upon contact with impurity? What is the ruling on non-Islamic products like perfume? And does impurity transfer simply by a defiled hand touching soap during washing?

As long as you are afflicted with obsessive whispers (waswas), do not rule anything as impure (najis) except with absolute certainty. Turn away from these whispers and pay them no mind. You are permitted to adopt the concessions (rukhsas) of the scholars, such as the view that alcohol is pure, and that ritual impurity does not transfer from an impure body to moist objects. The person afflicted with waswas may adopt the easiest of opinions to alleviate hardship. If you touch soap with impure hands, the running water will purify them. You must resist the whispers and maintain the presumption of purity unless you attain certainty to the contrary.