Cosmetic ingredient expiration dates
We recently did a webinar on cosmetic emulsions and asked people for questions prior to the event so we could cover the most important information. Here was an interesting question that came up which I think deserves an entire blog post. 
“If my raw material expires in 6 months, does that mean my cosmetic formula will expire in 6 months?”
Expired raw materials
To answer this question we have to first decide what we mean by an “expired raw material.” There isn’t a simple definition but you can think of an “expired” raw material as one which has chemically changed so much that it doesn’t behave the same way as the raw material you purchased.
This difference in behavior can mean different things. For example, it could mean that there are aesthetic changes that make the raw material different such as color or odor changes. It could also mean there are chemical changes that show up in measurements of pH, viscosity, melting point, refractive index, IR or Mass Spectrophotometer readings. Or the ingredient no longer shows activity in some specific test for example, sunscreen actives may no longer absorb UV radiation. It is these changes that go into setting an expiration date.
However, changes can happen gradually over many months (or years) so your company, or the raw material supplier, has to decide when a material has changed enough to consider it expired. Is a pH change of 0.1 units enough to consider a raw material expired? Probably not. Maybe a pH change of 2 units? Probably.There isn’t some magical date in which one day a raw material is “good” and the next day it becomes “bad.” You’ll have to determine what characteristic can change and by how much to make the ingredient unusable or “expired.” This will vary greatly depending on the stability of the raw materi
Setting an expiration date
The right way to set an expiration date for a cosmetic product raw material would be to determine what characteristics the ingredient must have for it to perform properly in the specific formulation in which it is incorporated. You would do stability testing at different storage conditions to predict how long it will take to see those changes. Based on these test results you could set an expiration date for a specific application.
This would be incredibly complicated.
Rather than do all that extensive testing for every raw material in every formulation, most companies just arbitrarily pick a date for which they consider an ingredient “expired.” This can be either 6 months or 1 year after the raw material is made.
Conflicting priorities
It’s worth noting that since expiration dates are mostly arbitrary, companies that buy raw materials are motivated to set long expiration dates so they don’t have to dispose expired chemicals. Companies who sell raw materials are motivated to have short expiration dates because you’ll have to buy more when the ingredient goes bad.
At my former company an “expired” raw material meant that the raw material had to be re-tested using the Quality Control tests originally run when the ingredient was purchased. If it passed those QC tests, they set the expiration date one year later and the material was no longer expired. This might seem dubious but we rarely had any product quality issues. Fortunately, most raw materials were used up quickly so we rarely did this.
Formulating with expired raw materials
This brings us back to the original question of whether your cosmetic formula will expire when your raw materials expire. The answer is…yes, and no.
Yes because if your raw material actually broke down and expired on the expiration date, the raw material in your formulation will likely also break down at the same rate. Depending on what is in your formula it may break down more quickly (or more slowly).
No because the original expiration date is arbitrary, and if your raw material met the QC specifications before it was put into your formula, you have no reason to expect that it will break down by that arbitrary date.
Determining formula expiration
One of the things I hope you realize by now is that expiration dates on raw materials and cosmetic formulas are complicated. Rather than relying on the expiration date of a given raw material, you should rely on the QC measurements of the important characteristics of that material. Then you should do a stability test of your formula to determine whether the finished formula maintains it’s quality over a certain period of time.
Then, with that information you set your own arbitrary expiration date for your product. Typically, we shoot for cosmetic formulas to be stable for at least 1 year.
But really, this is just a guess.
