Question: An Imaam (the one who leads congregational Prayer) of a Masjid (mosque) told me that if someone washes their head during the day of Ramadaan, their Sawm (Fast) will be broken because water will seep into the pores of the hair. What is your opinion on this subject?
Answer: Washing one’s hair while observing Sawm does not render that Sawm invalid. Water does not enter one’s body through the pores. Thus, whoever told you this is wrong as the Prophet (peace be upon him) used to wash his entire body while observing Sawm... read more here.