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What Does Oxidize Mean in Makeup? A Layman’s Guide

You look in the mirror on your lunch break. That foundation that looked so good on you when you left the house is now somehow…orange?? You’ve been walking around like this for how long? Horrifying.

You’ve been bitten by the oxidation monster.

But what even is oxidation? What ingredient in foundation causes it to turn orange?

I wanted to know, so I went deep into the internet woods to discover why. And I’m going to tell you all about what I learned.

(Here’s your usual disclaimer: I’m not a chemist. I’m not even a science major. I’m just a gal with a curious brain that loves me some research. If you’re a chemist and want to correct me anywhere, please go to my About page and email me!)

orange foundation on a brush
Source: Pegah on Pexels (altered by me).

What Does Oxidation Mean in Chemistry Terms?

Once, oxidation was defined as the reaction of compounds when introduced to oxygen. The dictionary still lists this as definition 1.

But now, scientists have broadened the scope of the definition (saying now it’s the process of losing an electron) because it turns out other things, like fluorine, can cause oxidation.

The takeaway? Oxidation happens when a reactive ingredient (yes, something in your foundation) is exposed to oxygen or another oxidizing agent.

What Does Oxidize Mean in Makeup?

First off, “oxidize,” when used in the makeup world, refers to a foundation darkening or turning orange after it’s applied to your face. This may happen in minutes or it may happen in hours.

According to my research, this darkening of your makeup is due to one of three things:

  1. The foundation ingredient iron oxide reacting to the oxygen in the air.
  2. Foundation ingredients being exposed to the acid mantle of your skin.
  3. Foundation ingredients being exposed to oils on your face.

Let’s talk about all these things separately.

Iron Oxide Reacting to Oxygen

Here’s some background: iron oxide (specifically iron(II) oxide) is an ingredient in almost every foundation, and it’s one thing that may be turning your face orange.

Yes, you remember your science right! Rust is a type of iron oxide. But the kind used in cosmetics has been deemed safe by the FDA, so no worries about getting rusty slivers on your face.

Iron oxide chemical formula
Iron oxide formula.

Here’s the interesting part: the ingredient iron oxide has already been oxidized. Otherwise, it would just be iron.

But here’s how I understand it. I imagine rust becoming increasingly bad as it gets further oxidized—turning more and more orange. Hopefully this will help you map what’s happening on your face.

Another thing to note: I saw some sites claim that other “oxide” ingredients, like titanium dioxide and zinc oxide, are also vulnerable to the same oxidation process. I found no evidence to support that they oxidize and turn orange (though they might react with your acid mantle—see the next section). Rather, I think these two ingredients are responsible for the white casts on your face in photos and for the white cast you get from mineral sunscreen—the opposite of creating a darker cast.

In fact, zinc oxide actually protects both itself and iron oxide from further oxidation, according to a freshman textbook on siyavula.com.

This leads me to conclude it’s the iron oxide—already orange and getting orange-er with exposure to oxygen—that’s responsible for true oxidation of foundation.

Let’s chat about the other two factors that may be contributing to the darkening of your foundation. They’re not techincally oxidation, but they could make your foundation change color in an unflattering way.

The Acid Mantle

First, let’s talk about your acid mantle. Yep. You have acid on your face!

The acid mantle is a protective layer on your skin, creating a barrier between you and bacteria. Since your blood is slightly alkaline (the opposite of acidic), any bacteria that do survive the acid mantle are less likely to thrive in your blood. After all, your alkaline blood presents the opposite kind of habitat the bacteria just made it past. (Thanks, Wikipedia.) Cool, right?

The pH scale running from 0 to 14
Source: Lisa Bronner’s very relevant post on “Skin Health, pH, and Dr. Bronner’s Soap”

The trouble is that the combination of metal oxides and acids causes all kinds of crazy stuff. There’s certainly a possibility of a chemical reaction on your face between the acid mantle and the oxides in your foundation.

It makes even more sense that the acid mantle is the culprit if a foundation oxidizes on you but not on your friend. Iron oxide is being exposed to the same air, so that’s not the problem. But maybe your friend’s acid mantle has a pH of 5.8 (less acidic) and your acid mantle has a pH of 4.8 (more acidic). You have more acid for metal oxides in your foundation to react with. Just a hypothesis.

Oils on Your Face

Oil bubbles on orange background
Source: @sharonp on Unsplash.

What happens if you open a powder compact and drip a few drops of oil in it? The powder will darken, right?

A similar thing can happen when your face starts to get more oily. If you notice a synchronicity between the time your foundation starts to darken and when your natural oils start to come through, it may be that the foundation is changing because its ingredients are mixing with your oils.

However, if you’re not an oily-skinned beauty, your issues are probably related to the iron oxide reaction with oxygen or with your acid mantle.

Make it Stop!

If you googled the why behind makeup oxidation, it probably isn’t because you’re loving the results.

So let’s talk about how to address these issues.

Addressing Iron Oxide Reacting to Oxygen

There aren’t a lot of great ways to prevent iron oxide further oxidizing. Avoidance and experimentation are the real solutions.

If iron oxide is anything but last on the ingredient list, meaning it’s of least concentration in the product, I’d be more cautious. Take a sample home, if you’re at Sephora. Also, be wary if you see something like this on your ingredient list:

The ingredient list on Maybelline's Fit Me Matte + Poreless with lots of different possible iron oxides included
The ingredient list on Maybelline’s Fit Me Matte + Poreless. Source.

It doesn’t specify where these pigments are on the ingredient list; it just says that it may contain them.

Perhaps you noticed that there were different iron oxides on that list, too. It may be worth some experimentation, if you’re getting samples. Take a picture of the ingredient list while you’re waiting for your sample and see if it contains a specific iron oxide, like the “CI 77491” listed above. If that’s the type of iron oxide in your foundation and you find yourself growing more orange with time while you wear that sample, maybe that’s the specific iron oxide to blame. Then, in the future, you can avoid foundations with that ingredient.

Addressing the Acid Mantle

As far as the acid mantle goes, you’ll want to look to your skincare to make sure your barrier isn’t too acidic. Look for products that are pH balancing.

Now, any company can just say their product will help balance your pH. They don’t have to prove it. So you may want to actually check the pH of the product.

You can read more about the ideal pH for the acid mantle on Banish.com (I found this article fascinating) and the aforementioned “Skin Health, pH, and Dr. Bronner’s Soap” from Lisa Bronner. You’ll find not everyone agrees, and I would have to research and write a whole new post to go over pH. Your best bet is to do a little digging yourself.

Note that oil doesn’t have a pH, so oil cleansing will never disrupt your acid mantle.

Addressing the Oils on Your Face

If you feel like your oiliness may be due to skincare needing tweaking, I’d look into that first. But if you were born oily and will be forever so, there are a few arrows to put in your quiver.

First, get a primer that puts a barrier between your skin and your foundation. Don’t get one that sinks in; this is the time to go for silicones (which, BTW, do not cause acne). We’re talking Benefit’s POREfessional or my fave, Dr. Brandt’s Pores No More Pore Refining Primer.

Pic of Benefit's POREfessional
She’s here to help with your foundation-darkening woes. Source.

This will slow the process of your oils and your foundation blending.

Second, try blotting and powdering before you get overly oily. Keeping your oils at bay the best you can will also help put off the darkening that can come with oils blending with foundation ingredients.

Summing Up and Recommended Read

So there we have it! What does oxidize mean in makeup? Well, from my research, it means that:

  1. The foundation ingredient iron oxide is reacting to the oxygen in the air.
  2. Foundation ingredients are being exposed to the acid mantle of your skin.
  3. Foundation ingredients are being exposed to oils on your face.

In this article, we discussed these three things in detail. And we also covered how to address them with avoidance, experimentation, a skincare change up, and oil control.

One last thing, and it’s a plug for another blog you may find helpful. During my research for this article, I found myself on various pages on the Beautiful with Brains site. I highly recommend strolling around there. You’ll get more info than what I shared here about all sorts of topics related to this article, like pH and oil cleansing. I also recommend reading this article from Project Vanity. You’ll see a different opinion than mine at times, but it’s a good way to build on what you read here and come to your own understanding.

Now go forth and banish the orange from your life!