- good skin or hair feel
- substantitive to skin or hair
- how it performs in hard water
- foamy resistance to soap and/or sebum
- how to thicken it
These qualities will make it clear which one is good for which application. For an oily hair shampoo, you'll want to have good resistance to sebum, otherwise your lather will fail! For a bubble bath, you want bubbles, bubbles, bubbles, and a good flash foam. For a body wash, you want mild cleansing with a moisturizing feeling. And so on.
All detergents will irritate our skin, no matter how mild they are. (Yes, even cold process soap because the very nature of putting a detergent-y surfactant of our skin means we are removing oils, and our skin doesn't like that! Heck, even water can irritate some skin types!)
Data bulletins for the various surfactants will generally list how much active ingredient is required for mild to moderate skin irritation. Most are quite high - for SLeS we need 40% in a mixture to get mild to moderate skin irritation - but some, like SLS, are lower (at 35%). So if this is a concern for you - and you don't get the information you need in my post - click on the data bulletins I'll be including for at least one brand of the appropriate surfactant in the post.
So for judging detergents, it's safe to assume that most - if not all - are considered mild cleansers when it comes to personal care products. I'll be using a scale that's a little annoying - sorry, but they all want to be considered "mild cleansers", so we need to re-define the word! Think of it on a scale from 1 to 3 (but I hate using numbers, so you won't see "1" or "3" in my posts!)
- Gentle or very mild - this surfactant is unlikely to cause skin irritation when used at the suggested amount or lower. It is unlikely to bother your eyes as well.
- Mild - this surfactant is unlikely to cause skin irritation when used at the suggested amount or lower, but don't get it in your eyes. It could cause irritation for people with very sensitive skin.
- Not so mild - this surfactant may cause mild skin irritation when used at the suggested amount or lower, and it may cause eye irritation. It could cause irritation for people with sensitive to normal skin. The only one that falls definitely in this category is SLS.
I've only just started this series and the word "mild" is already looking funny to me!
Join me tomorrow as we embark on the exciting journey through world of surfactants!