Purity: Doubt Regarding Obstacles on the Body
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 377:
While performing ghusl, if one rationally deems it probable that there is something on his body that may be an obstacle for water to reach the body, he must examine it and become confident that it is not an obstacle.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)