Order of operations: a delicate balance

Do you remember PEMDAS? It’s an acronym that we used in math class to remember the proper order of operations: Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction? Or, Please Excuse My Dear Aunt Sally (Poor Aunt Sally, what did she ever do to deserve being excused?).

Well, the order of operations is much less clear when it comes to skincare products. What’s the most effective way to apply your products? Do certain ingredients cancel each other out? How many active ingredients is too many?

I’ve been pretty happy with the results of my normal routine thus far, but I bought The Ordinary Mandelic Acid 10% + HA and The Ordinary Azelaic Acid Suspension 10% at the Deciem store last week for a reason: I was curious if they could help my skin improve even more. At the same time, I’m also afraid of messing up the status quo, so I decided to ask the experts at Deciem for tips on incorporating these two new items into my existing skincare regimen. I mentioned which two TO products I bought, and that I currently use Differin at night, and a Vitamin C moisturizer.

The current state of operations

Here’s some background on my current skincare routine, pre-The Ordinary.

My normal skincare routine:

AM:

• wash face with 365 Everyday Value Gentle Skin Cleanser
• Australian Gold Botanical Tinted Face Sunscreen SPF 50

PM:

• CVS Just the Basics pre-moistened facial towelette
• 365 Everyday Value Gentle Skin Cleanser
• Thayers Alcohol-Free Cucumber Witch Hazel Toner
• pea-sized amount of Differin gel
• small spoonful of Frudia Citrus Brightening Cream on face and neck

Deciem’s response to my question

Deciem responded within 48 hours with the following message:

For some reason the first sentence was in the past tense, while the rest was in present tense. Weird?

My main takeaways from The Deciem’s response

If you’re using a Vitamin C moisturizer and Differin, you can incorporate TO serums and emulsions in there as well, but keep the following guidelines in mind:

• Don’t use more than three serums and emulsions at any one time, for “optimal skin penetration”
• The Ordinary Azelaic Acid Suspension 10% is classified as an emulsion/suspension, so it should go after any water-based formulas like TO Mandelic Acid 10% + HA
• alternate active ingredients (direct acids, retinoids, and vitamin C)—do not apply them together
• vitamin C moisturizer can be used in the daytime or at night
• Azelaic acid can work in the daytime, but if you use it in the daytime, don’t combine with vitamin C

A little of The Ordinary goes an extraordinarily long way

Interestingly, Deciem recommends applying a smaller portion of products to your face and neck than I thought. This makes The Ordinary products even more affordable than I thought.

The message above recommended applying just a pea-sized amount of emulsion/suspension products like TO Azelaic Acid Suspension 10%, and just 2-3 drops of serums like TO Mandelic Acid 10% + HA. These portions “should be enough” to cover the face and neck.

This means that my little 30-mL (1-oz.) bottle of Mandelic Acid is going to last a long time. According to a Google search for “How many drops are in 1 oz?” the answer is ~591, or 197 three-drop servings. Plus, if I only apply it one-third of the time at night, it’s going to last about a year and a half. The Azelaic Acid Suspension 10% is also a 1 oz. bottle. A pea-sized amount is supposedly about 0.25 grams, or 0.009 ounces. One ounce will yield about 111 pea-sized portions. However, this National Institute of Health study found that adults tend to overestimate how big a pea-sized amount should be (at least, in the case of toothpaste). I’m pretty sure that I have been using a cannellini bean-like amount thus far, so I think I also tend to overestimate how large peas should be. So I will probably not be able to get 111 doses out of the 1-oz. bottle. But that doesn’t mean that you can’t!