Prostration, putting forehead on the ground or clay-tablet, has many medical benefits. But some reports showed on the forehead of a few prayers it causes prostration effect/PE or clay-tablet effect/CTE, as a skin-callosity, on his/her forehead. This effect, which in Persian language is named Mohr-e-Pishani, has always been a curious question for researchers. Observation of the PE raises many questions in mind, which is not limited to the present time. For example; in old books 'Ali Ibn Al Husayn, Zainul Abedeen (PBUH), the fourth Imam of the Shia, has been nicknamed " Dhu Althafanat" for having the CTE on his forehead which in the Arabic language means “the owner of skin-callosity”. The main purpose of this study was to uncover the scientific evidence of the PE on the forehead of some prayers. The results showed that several factors would result the development of PE, including physiological factors such as skin structure and its keratin content; allergens of the ground and soil as an external factor including chemical elements, acidity, macromolecules, and microorganisms. Physical factors, such as the way and duration of prostration, head weight concentration on the ground, soil or clay-tablet are also effective. These findings can answer some of the questions, curiosities, and possible doubts related to the phenomenon of PE or CTE on the forehead as a phenotype for other researches.
