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What factors improve the lotion/cream stability?
I wonder that what factors contribute to the stability of lotion/cream?
Thank you so much in advance for inputs to this topic. -
30 Replies
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Off the top of my head…
- Particle size when you first make the emulsion
- Compatibility of emulsifiers and oil
- Amount of water, oil and emulsifiers
- Having a suspending agent
- Environment your emulsion is exposed to
- Efficacy of your preservative -
@Perry. Thanks a lot. Can you explain more details on each your input topic. For example, what is “Particle size when you first make the emulsion”?
Thank you so much Perry
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I would add making sure anionic ingredients are not mixed with cationic. Made that mistake not so long ago.
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Thanks
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Again, way too large a topic to safely handle piecemeal like this. Basically, you are asking for a summation of Emulsion Science in several paragraphs.
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@Microformulation can u explain “way too large a topic “ . I don’t understand it
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I think what Microformulation says is that it would take pages of text to address every bullet point Perry listed above. This is a very broad topic. I recommend you to subscribe to swift crafty monkey blog. She explains chemistry in a simple language.
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Oh, thanks @ngarayeva001.
For the fading dark spot cream in the market, how long does it take to get rid of the dark spot? -
@Dtdang, I don’t want to sound dismissive, but it’s a separate topic.
But in general, you need to know what kind of dark spot is it. Is it a sun spot? Is it an acne spot? Is it a melasma? I am afraid that if it’s a melasma, even hydroquinone migh not help with and you would need a laser treatment (that also might not help if it’s deep enough in the dermis). As an example 2% alpha-arbutin by The Ordinary helps me get rid of freckles that I get from a relatively short term sun exposure in a month. Again you can’t use it as a rule, it’s a personal experience. I am sorry but the simple answer doesn’t exist.
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@ngarayeva001 thanks for answering. It is so complicated one. I agree with you to post it as separate one.
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Active ingredients is a separate topic, but you still need to know how to create stable emulsions. That requires a lot of reading and even more experimenting. I am not saying that I know everything about it myself, but I learned through a trial and error. Try to make a lotion, fail in it and start reading to understand why you failed. Change the inputs, repeat. Run tiny bathces, like 50 grams not to waste ingredient. Fail, try again and write down what you did to analyse.
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@Dtdang In a University setting, Emulsion Science (the discipline which covers all your questions) is a Full Semester course. As such, how can it be covered fully and effectively in a group like this?Perhaps you could start looking into Stokes Law and Emulsion Stability as a beginning.
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@Microformulation, @ngarayeva001thanks a lot.
The Stoke’s law that makes sense for research? Not practical? -
I agreed that emulsion processes are trial and errors. Therefore, I create this topic in order to improve our knowledge
1) main emulsifier + co-emulsifier, thickener, anti-bacteria oil, preserve
2) mechanical processes: high speed stirring,
3) airless container -
I can promise you that no formulator is doing calculations with Stoke Law while formulating. Is it even worth knowing to become a cosmetic chemist? Probably not. The textbooks on cosmetic chemistry are good but some throw a lot of equations at you that are relevant but not in a practical setting. And I find Perry’s answers satisfactory.
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Even calculated HLB isn’t a guarantee of the success, however it’s important to know certain rules.
I understand that professionals are getting very frustrated when someone asks for an easy solution, which clearly doesn’t exist. However since the majority of the members of this forum are not chemists, it’s important not to discourage people from learning.
@Dtdang, overall you are right, but there is no such thing as anti-bacterial oil. You need an emulsifier compatible with the oil (if the emulsifier is nonionic calculate the HLB), you want to make sure the oil is stable (not going to get rancid), you want to add your antioxidant, broad spectrum preservative and chelating agent and yes, airtight container makes everything better. -
@ngarayeva001 completely agree.
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@Christopher and @ngarayeva001 thanks you so much
I agree both of you. -
We learned Stokes Law in College as a way to theoretically address the factors which affect stability. It is a theoretical method to address all the issues of an emulsion. It is not used in real time.Is it worth knowing to be a Cosmetic Chemist? YES. In fact, Kelly Dobos did a posting on it and its use in Chemist Corner in the past.Look at Page 3 of this knowledge base article. What do I see? Stokes Law as a predictor of Cosmetic stability. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=2ahUKEwiE-JTwsNvdAhXIuVMKHaKCDCcQFjAMegQIYBAC&url=http%3A%2F%2Fwww.essentialingredients.com%2Fpdf%2FHow%2520Do%2520I%2520Thicken%2520my%2520Cosmetic%2520Formula.pdf&usg=AOvVaw2OzdXLWzUCcVEgpELAadt3
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Look at the equation. If you relaize that obviously you can’t change gravity (g), you can see that controlling particle size (r) is an important aspect that can be controlled. The viscosity of the continuous phase (μ) contributes to the stability. In an oil in water emulsion, this is the aqueous phase.The take-away is that you can;- Ensure that your process engineering and the manufacturing process are designed in such a way to create the smallest possible micelle (r).
- Use a rheology agent such as a Carbomer to increase the viscosity of the continuous phase. Many think they use a carbomer in the water phase to “thicken” the final product, but as you can see in this case the carbomer properly acts as an “emulsion stabilizer.”
THERE is the usefullness of a modified Stokes Law as a model to identify the factors in emulsion stability and to educate on the factors which you can modify in order to maximize stability.So, it is a great educational tool. It is not used in day to day Formulating like total solids or HLB.So, not so useless. -
@Microformulation, I had no intention to say that the right
scientific approach is useless. But its different levels of knowledge we are
dealing with here. Many people here are making lotions the same way they would
bake a muffin. When I just started I bought literally the first
“ewax” available on amazon, mixed it with cold water, dumped
some oil in that concoction and was utterly amazed when it didn’t emulsify. Now
I am reading more or less serious papers, doing my research on the active
ingredients and make more advanced mistakes, like mixing amphoteric surfactant
with anionic and bringing pH below 6 (I am a dilettante and I know it).
People learn through trial and error, and yes hard core science is the best,
but you can’t teach differential equations to someone who doesn’t know arithmetic
yet. It would just demotivate them. Disclaimer, I personally appreciate your
comments and learned a lot thanks to you. -
Speaking about dilettants, @Microformulation, may I ask you to through some article, on how to design the process the way to to create the smallest possible micelles, at me :smiley: My first real overhead stirrer (yay!) is coming on Friday.
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@ngarayeva001 - I agree that we don’t want to discourage people from learning but there are two points to consider.
1. I’m not sure it’s accurate to say the majority of people on the forum are not chemists or scientists. They just aren’t as vocal and are more often lurkers. I’d guess most of the members of this forum have a science background (although they probably aren’t cosmetic chemists specifically).
2. People who post questions do have a responsibility to do some preliminary investigation of their question at the very least. This forum should be for questions that can’t be easily Googled for an answer.
A quick Google Search of “emulsion stability” leads to this nice slide presentation on the topic.
https://www.slideshare.net/akarim717/emulsion-stability
And there’s even a helpful video explaining emulsion stability.
https://www.youtube.com/watch?v=y_696sKwISI@Microformulation has provided a deeper explanation for the initial question which is an answer that wouldn’t be obvious by doing a simple Google search.
I personally don’t mind answering pretty much any question, so I say keep them coming.
But I can understand how other cosmetic chemist & formulation experts get annoyed when the questioner hasn’t seemed to have even done the bare minimum investigation into the topic.
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Thank you @Perry. My bad, I shouldn’t have generalised this way. I just keep seeing many not very advanced questions, that’s why I said “majority are not chemists”, which is most probably not the case. I admire your patience sometimes, as I noticed that you answer questions even more basic than the emulsion stability. I totally agree that people should do their research first. I have been reading this forum (blog and podcast) for many months before I decided to join as a member and started asking questions. That is why I highly encourage hobbyists to subscribe for blogs that explain chemistry in a simple language, analyse LOIs of commercial products and experiment. Sometimes people don’t know where to start and unfortunately do not have access to many basic cosmetic ingredients.
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@Perry My issue is not that I get annoyed, but rather that a good literature search and directed study is exponentially more effective than just asking questions piecemeal. The hit and miss approach does nothing to create a well-rounded Formulator.My first position after school I worked with several experienced Chemists who were ultimately great mentors. They outright refused to answer questions in a hit and miss matter. They would challenge me to find the answers myself. Ultimately in each case, I learned FAR more than I would have with a simple answer and the next day my questions were much more useful, advanced and deeper than my initial question. Later on in life, I found the best Techs and Chemists were the ones that engaged in reading on their own part. I was always glad to see them advance faster and oftentimes even teach me an aspect of the issue.Anything worth doing is worth doing right.
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