I've been reading up, trying to tell what makes a 'shampoo bar' which has no SLS and no other detergents and is, in fact, made entirely with oils/fats and lye, a "shampoo" bar and not a soap. I know there's an emphasis on it washing away cleanly and not leaving a residue; are there only some recipes which produce a bar suitable for hair as well as body, or is this an advertising ploy, and any handmade soap (with all its natural glycerin intact, etc.) fine for hair?
Is there a well known answer to this, or is it the subject of debate and individual preference?
Thanks in advance for any clarifying information or educated opinions.