Sunday, December 30, 2012

Comedogenicity: What the heck does that mean?

What does comedogenicity mean or what does it mean when an ingredient is comedogenic? It means that an ingredient or product causes the formation of comedones (blackheads) in a relatively short period of time. Blackheads form when the outer layers of our skin do not shed properly and the hair follicle is blocked. The blackhead part comes from the oxidation of fatty acids on the surface in the skin. Scienticians still aren't really sure what causes this lack of desquamation. Formation of comedones are not accompanied by skin redness.

Most of the scores we see for comedogenic ingredients come out of the rabbit ear assay or rabbit ear model, which is a test in which "the test material or an extract is applied directly to intact and abraded sites on the skin of a rabbit. After a 24-hour exposure, the material is removed and the sites are scored for erythema and edema." (redness and swelling). This link. As in the name, the tests tend to be done on the rabbits' ears. 

There is a lot of controversy about the rabbit ear model and its application for human skin. As this article notes, this debate is not new as different models show very different comedogenicity levels for the same ingredient. This textbook notes that "Lists of comedogenic ingredients are not necessarily meaningful" because they cannot predict the comedogenicity of the final product as the concentrations used on in tests aren't the same as those used in a product, like a lotion. We've seen how some ingredients can lower the comedogenicity level of other ingredients - for instance, using 1% to 10% mineral oil with IPM can reduce its level from 3.6 (out of 4) to 1.3 and 25% can reduce it to 1 - and we've seen that some ingredients are considered really comedogenic on one scale and not at all on another, like shea butter. 

Having said this, rabbit ear testing is being phased out or has been forbidden (EU) and we're seeing more testing by biopsying the back skin of human volunteers who have been shown to form comedodones easily. (Reference). It's hoped this will produce more accurate scales of comedogenicity. 

Is mineral oil comedogenic? Not according to this study. "Greasiness cannot be equated with comedgenicity. The admonition forces acne patients to seek "oil-free" skin care products has no scientific merit with regards to comedogenicity. Cosmetics are an unlikely cause of the relatively high prevalence of post-adolescent female acne." Wow! That's pretty amazing, eh? Now, this was published in 1996 and there may have been some studies done since then, but I think it's a pretty amazing study in itself! Check out also this study Is Mineral Oil Comedogenic? which came to the same conclusions. Apparently the perception that petroleum products were comedogenic came from a time when the ingredient was poorly purified and traces of tar - which is comedogenic - would be found. This doesn't happen any more. 

What does all of this mean? Keep an eye out for those ingredients that seem to make your skin worse! If shea butter is listed as a 0, it doesn't mean that it won't cause you problems, and wheat germ oil (a 5) won't necessarily bother your skin. Keep a record of these ingredients. This is one of the reasons I suggest keeping your initial formulations simple - using five different oils might seem awesome, but if you break out or hate it, it's hard to figure out the culprit. 

Also keep in mind that comedogenicity isn't just about oils. Ingredients like surfactants or humectants can cause issues as well. (See this study on the safety of sodium PCA - it is not considered comedogenic.) Some studies I've seen suggest that harsh detergent based cleansers can be worse for acne prone skin than applying oils! 


Christopher said...

Basically every ingredient that exists can break us out, even if it's not considered comedogenic. It's kind of off putting when you think about making your own cosmetics. Let's say you only use 1 oil (like you advise us to) you might still break out from the other stuff in it. So it can take forever to determine what is breaking you out. I guess you could try an ingredient alone on your skin, but I'm kind of weary of this as well.

Susan Barclay-Nichols said...

I have a few posts on acne prone skin in the skin chemistry section of the blog. Check those out and see if I address your questions there!

This is why making facial products is a lot harder than body products. I break out from pretty much any oil on my face, but I can handle everything on my body. It is one of the reasons coming up with even a basic moisturizer can take ages. Most other things we can learn from others, but ingredient sensitivities are something we have to work hard to figure out, and it can take some time. But it is worth it!

Anna said...

So I was just wondering if there was somewhere you could find out how comedogenic different fatty acids are?

I would like to be able to figure out how comedogenic an oil is just by knowing its fatty acid composition.

I have tried to find an extensive list of how comedogenic fatty acids are an google, but failed, so I thought you might know a good book or wesite?

Susan Barclay-Nichols said...

Hi Anna. I don't think you're going to find one as comedogenicity isn't simply function of the fatty acids in an ingredient. For instance, sunflower is considered an 0 while grapeseed is a 2, and soy bean oil is a 3, all of which have high levels of linoleic acid. Shea butter is considered a 0 while cocoa butter is a 4 and they share the same fatty acids in very similar ratios. And there are loads of ingredients that are considered comedogenic that have nothing to do with fatty acids, like surfactants and esters.

As an aside, comedogenicity lists aren't really all that accurate. They were based on rabbit ear tests, which aren't as accurate as we think. Take a look at this post I wrote on the topic to see more about this controversy.

Good thoughts!

Anna said...

Aah, I see! Thank you for clearing that up for me!

Elise May said...

Hi Susan, I'm curious to know what you think about algae extracts being comedogenic. In the acne world I hear this a lot from bloggers and practitioners, but I can't find any actual research or sources on this. Thoughts?

Susan Barclay-Nichols said...

Hi Elise. I don't know what kind of algae extracts you are referring to, so I'm afraid I can't be helpful. If they are hydrolyzed proteins, then I don't think they are comedogenic. Sorry I can't be more helpful!

Elise May said...

Hi Susan, let's say red algae extract. Any thoughts on that being comedogenic or response the same? Thank you!

Elise May said...

Hi Susan, let's say Chlorella Emersonii (Red Algae) Extract. Any thoughts on that being comedogenic or response the same? Thank you!

Susan Barclay-Nichols said...

Hi Elise May. I wasn't able to find much on this topic, but here's a study that might interest you. Acne and Chlorella lipids. Interestingly, it seems to be only found in a few products, including a sunscreen that came up on my search.

As a note, it's hard to say what is comedogenic or not these days. The standard test on the rabbit ear isn't really valid for people. It really is all about trying things and seeing what happens. As well, it depends on if you are acne prone, rosacea prone, and so on.

Elise May said...

Thanks so much for your help, Susan. You are such a wonderful resource! :)