What is the ruling on the filth that accumulates on the body and is difficult to remove, and is it a result of body perspiration or underwear?

If dirt, originating from outside the body, prevents water from reaching the skin, it must be removed for the purification (taharah) to be valid, though a small amount is excused. However, if it does not prevent water from reaching the skin, it does not affect the validity of the purification. If the dirt originates from the body itself, such as dried sweat, the purification is valid even with its presence. One must be cautious of obsessive doubts (waswasah) and adopt the easiest interpretations.