My long term Twitter chum Musical Houses raised a problem she has with some cosmetic ingredients with me over Twitter, using no less than 8 tweets to do it. Such patience clearly deserves an answer.
Hey Colin! Wanted to email you via your Problems Page but I guess your form must be super spammed! I don’t remember much of what I learnt in Chemistry, but I’m wondering: Say my skin doesn’t do well with isopropyl palmitate and isopropyl myristate in high amounts in skincare. Does this mean things like Myristyl Myristate, or [Something] Palmitate/Myristate would be likely to have a similar effect on my skin too? I vaguely recall that maybe the palmitate/myristate part is from the acid part of the fatty acid, and the Isopropyl part is from the alcohol, so I’m wondering if there’s a simple way to deduce if other esters with either the same alcohol or acid part are likely to behave similarly on my skin? And if my skin doesn’t do well with those ingredients, is it more likely due to the alcohol part or the acid part? Not sure if my line of thinking s correct? Sorry for the unclear wording (obviously not extremely articulate in technical matters)!
No need to apologise, it was very clear. And you have remembered your chemistry pretty well too. Esters are indeed made up by combining an alcohol and an acid. So for example isopropyl myristate is created by reacting isopropanol and myristic acid. Isopropanol is a thin volatile highly flammable solvent. Myristic acid is a white solid waxy material. But isopropyl myristate is an oily liquid with a velvety feel on the skin. It isn’t at all obvious how its properties derive from the components from which it is composed.
The usual example given to show that compounds don’t resemble their constituents is common salt, which everyone knows is composed of sodium and chlorine but doesn’t look anything like either. It isn’t quite so extreme with organic compounds – you can sometimes pick up common behaviours from common groups. But nonetheless it is usually a mistake to look at the names of chemical compounds and think that because they have similar names they will have similar properties.
In the example you give, myristyl myristate is the ester of myristic acid and myristyl alcohol. This is quite different from isopropyl myristate in many ways. For a start it is nearly twice the size so it is likely to be a lot slower getting across the skin.
So if it is simply that the esters you have a problem with just happen to react with your particular skin in some way, there is no real reason to suppose myristyl myristate will do the same.
But skin reactions are sometimes the result of allergic reactions and allergic reactions are often the result of the skin being sensitive to a particular part of a molecule. So it is possible that your problem is with the myristyl bit – in which case myristyl myristate might well be a problem. If it is with the isopropanol bit you’ll be fine. And if it is with the ester link then you’ll have a problem with both this and lots of other widely used cosmetic ingredients. The only way to find out is to try different formulations on study the ingredients closely. (I think you do that anyway.)
Sorry I can’t be more specific but thanks for the question.