A while ago I came across this article dismissing HLB for organic/ natural cosmetics and suggesting that ‘Anyone who encourages you to calculate the HLB of your emulsifiers will be mainly used to working with synthetic emulsifiers’. Reading this triggered me to respond as all I can see is a (quite possibly unintentional) dumbing down of cosmetic chemistry. It may even demonstrate a lack of understanding of the value of the concept in understanding how a formula is structured.
Here's my input.
While it is true that HLB theory as it applies to cosmetics was developed when ingredients and cosmetic emulsions were simpler – typically non-ionic (synthetic) emulsifiers designed to hold mineral oil inside water, the scientific rationale behind the theory still holds true and I personally use HLB theory every time I make a cream, a spritz spray or non-ionic containing surfactant based product (very common for organically certified formulations).
So what does HLB theory teach us?
HLB = Hydrophille, Lipophille Balance.
It tells us quite a lot about:
The structure of the ingredient - is the water or oil-loving part dominant?
Where will the ingredient sit?
What type of relationships will it form?
Is that what I want for this formula?
HLB numbers remain a useful and convenient tool for the cosmetic chemist to visualise where and how a surface-active non-ionic molecule will orientate itself in an oil and water mix. In my case, this helps me to quite literally draw out the relationship between my oil and water phase by giving me a big clue as to what is going to go where.
HLB helps me to predict surface tension and spreadability, skin feel, emulsion viscosity and type, the rough size of the oil drops in an emulsion and whether a secondary emulsifier might be needed and if so what. The fact that oil phases are more complex these days thanks to our love of vegetable oils over mineral oil does not make the theory irrelevant, it merely means we have to understand the chemistry of our oil phase more to work out if there is anything else we need to consider such as the oil phase polarity or potential to degrade (oxidise).
Mineral oil is completely non-polar making its behaviour easy to predict in an emulsion.
Vegetable oils are classified as broadly non-polar but their
Likewise, the fact that our emulsifiers now come in all shapes and sizes with polyglycerol esters and glucosides growing in popularity we also have to consider the size and shape of these AS WELL AS their HLB rather than just ditch HLB altogether. However, the fact that surface-active agents with low HLB (3, 4 and 5) favour the oil phase over the water phase and surface-active agents with high HLB (11, 12, 13, 14, 15) favour the water phase over oil and those in-between are like the diplomatic peace corps of the emulsion world and like to spend time with each phase still applies.
So why would people say that HLB isn’t important any more?
Ingredient manufacturers have been doing the hard thinking for us since the late 1990’s and early 2000s when self-emulsifying waxes first became available. These waxy blends typically consist of cetearyl alcohol with a high HLB ingredient that can just be added to the oil phase without the need for further calculation or thought. The high HLB part of the blend is the primary emulsifier and produces an oil-in-water mixture while the cetearyl alcohol helps to structure the oil phase creating viscosity and further stability. Cetearyl alcohol actually helps to form a liquid crystal structure in the product which is why its presence causes the emulsion to gain viscosity. Not that everyone appreciates that of course because these days we don’t have to think……
So yes, cosmetic chemists of today DO NOT NEED to calculate HLB or draw diagrams to work out what is going to end up where BUT that doesn’t mean that the knowledge and understanding of HLB is no longer required.
What if something goes wrong in the formula?
What if you want to improve the formula or make it cheaper or more effective?
What if you want to make something different like a micro or water-in-oil emulsion?
As much as I love and use these self-emulsifying waxes to make emulsions I can see their downsides. We now have a generation of cosmetic chemists who have never had to think about what HLB means and NEVER had to apply it. I find this quite the tragedy and wonder where this dumbing down will leave us a few more years from now.
For me, a cosmetic chemist who is content with not understanding HLB theory is akin to a chef who is satisfied with making a cake from a packet mix while telling everyone they are great at baking. Convenience shouldn’t replace knowledge, it should just empower it.
So I can’t agree with the premise that the HLB system is irrelevant and can be dismissed and I absolutely can’t agree that people who talk about it are ‘old school’ and ‘not used to naturals’.
But then I would think that because I believe that an appreciation of chemistry will save the world.
So that’s that.
PS: And yes, I do know that not all emulsifiers are non-ionic and that HLB theory wasn't developed to apply to those but that also doesn’t make HLB theory irrelevant. Thanks 🙂