Valentine’s? More like Valen-time to get some new lipstick!

With Valentine’s Day right around the corner, I can already smell the … lipstick? So, you may be wondering why I am talking about lipstick and not something normal, such as chocolate or flowers. To answer that question, let me take you back to a few days ago in front of my bathroom mirror. I was perusing through my makeup collection and found the perfect lip colour for that ever-fateful Valentine’s date. Not only did this colour match my skin tone, but also my outfit of choice for the big day. However, just as the lipstick was getting closer to my lips, my nose took the first blow. An almost violent stench stormed its way through the air and into my nostrils. My mind could not even begin to comprehend that such a smell could emanate from my makeup products, but as everyone knows, cosmetic products do eventually expire.

With my despair fresh in my mind, I decided to bring this topic into the workplace the next morning. I was met with brand new information (to me at least) from my colleagues, who explained that cosmetic products will expire anywhere between 6 to 36 months after their opening. After a brief investigation, I found that cosmetic products are mainly composed of lipids and some sort of pigment for colour. Generally, it is the pigment that plays the role of the villain and makes the cosmetic product highly susceptible to oxidation.¹ This oxidation can then lead to the formation of aldehyde products, which are generally highly reactive and toxic to the body.² Luckily (or maybe unluckily), there is a definitive way to tell when your product has gone bad. These aldehydes formed through oxidation reactions can give your cosmetic products a rancid taste (when applied to the lips) and smell.¹ Good thing I didn’t end up tasting this abomination.

While I was certain that my lip product has gone rancid, I wanted to determine if I could confirm this through benchtop nuclear magnetic resonance (NMR) spectroscopy. Aldehydes have a characteristic ¹H signal that ranges from ~9 ppm to 10 ppm, so if I could observe this, then this would be strong evidence that my lip product has gone rancid. In my conquest, I followed a slightly modified procedure previously described by Lachenmeier et al.¹ Figure 1 shows the ¹H spectra of the CDCl₃ extract of this product at 60 MHz (left) and 100 MHz (right).

Figure 1. ¹H (60.7 MHz and 102.3 MHz) NMR spectra of lipstick extracted in chloroform-d with an inset zoom of the characteristic aldehyde proton peak. The asterix represents the residual solvent signal for chloroform.

To nobody’s surprise, the cosmetic product was predominantly composed of oils, but at 9.84 ppm, we observe a proton that is likely associated with the aldehyde functionality. As a side note, if you are interested in assigning the chemical shift regions of this oil, we have a spectrum of different edible oils here and an application note about the adulteration of olive oil with soybean oil here. As evidenced by the spectra in Figure 1, the 100 MHz instrument exhibits superior peak dispersion, which is best seen in the region between 4-5.5 ppm. However, since we’re specifically looking for an aldehyde signal with a relatively remote chemical shift, we can observe this at both fields. It’s interesting to note that the aldehyde peak at 100 MHz appears to have a subtle shoulder, which might be indicative of more than one aldehyde species in solution.

Needless to say, that lipstick product has now been terminated. Now, if you are ever wondering why your makeup product is smelling a certain way or is giving you an ‘off’ sensation after application, then maybe it has gone rancid. If you enjoyed reading about my misfortune, we recently published a blog on Santa’s favourite cookie here and a blog about spices here! As always, if you have any questions, please do not hesitate to contact us! That’s it from me, I hope you all have a wonderful Valentine’s Day whether you celebrate it or not!

References
[1] Lachenmeier, D.W.; Gary, M.; Monakhova, Y.B.; Kuballa, T.; Mildau, G. Spectrosc. Eur. 2010, 22, 11-14.
[2] Laskar, A.A.; Younus, H. Drug Metab. Rev. 2019, 51, 42-64.