Do the use of gels and creams, whose composition includes chemical substances, and washing hair with soap and hot water, cause harm and are they prohibited?

If it is established that using gel and creams causes significant harm, then it is not permissible in Islamic law to use anything that causes harm, due to the Prophet's (peace and blessings be upon him) saying: "There should be neither harming nor reciprocating harm," and because the fundamental principle for anything harmful is prohibition.