Reveal even, smoother, glowing skin with this 5% Lactic Acid + Hyaluronic Acid Exfoliating Serum formulation. Gentle AHA lactic acid offers mild chemical exfoliation, backed up with a blend of skin-soothing and hydrating actives to reduce inflammation potential and keep your skin hydrated and happy. I’ve had a ton of requests for AHA (alpha hydroxy acid) formulations over the years, and today I’m finally sharing one—I hope you like it!

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To start with: this is not a beginner formulation. Stirring the ingredients together isn’t challenging, but you need to be comfortable testing and adjusting pH to a fairly precise level to make this. This isn’t a particularly hard skill, but it takes practice, and if you’re a brand new maker I know it can seem intimidating. You’ll also need a digital pH meter, which is not an insubstantial investment. If purchasing a pH meter and pH testing/adjusting seems daunting to you right now, no worries! File this one away for the future, when you’ve got a bit more experience and have the budget for a digital pH meter. In the meantime, the 5% Lactic Acid product The Ordinary makes is lovely and inexpensive 😊

The AHA used in this formulation is lactic acid. Lactic acid is a naturally occurring part of our skin’s natural moisturizing factors, and is generally considered to be one of the gentlest AHAs. You’ll also find lactic acid in milk, but the stuff we use in cosmetics is synthesized and vegan. My lactic acid is a 90% solution from Voyageur Soap and Candle Co.; it looks like they’ve changed what they sell since I purchased mine as they now only have 88% lactic acid. If your solution is 88% instead of 90% you’ll need to use a bit more to keep the final percentage of lactic acid at 5%; I’ve included precise numbers in the Substitutions list at the end of the formulation.

Alpha hydroxy acids (AHAs) are, as you might’ve guessed, acidic! Even low concentrations will cause the pH of our formulations to become very acidic, so in order to prevent skin damage and irritation we need to raise the pH with a base. The CIR stipulates the pH of AHA products should be above 3.5, while the pKa values for lactic acid and glycolic acid mean a pH around 3.8 is best for formulations made with those acids for the optimal balance between efficacy and irritation potential (read this article from Lab Muffin to learn more!). Sodium hydroxide (NaOH, also referred to as lye) is the industry standard ingredient for increasing pH; you’ll find it on all kinds of ingredient lists for AHA products (Examples: 1, 2, 3, 4, 5). It can be surprisingly high up the ingredient list! To use NaOH to raise pH you’ll want to create a 10% solution of it (remember your gloves and eye protection!) by mixing 1 part NaOH and 9 parts distilled water (by weight). I typically create 10–20g at time as you don’t want to keep this solution around too long or the pH will drift upwards. I’ve included 1% of a 10% NaOH solution in the formulation to kick-start raising the pH, but you’ll need more. Precisely how much more will vary with the pH of your distilled water and if you make any other changes to the formulation. Determining that precise amount is the tricky part of this formulation. If you’d like detailed guidance on this, I’ve created an exclusive video for my $10 and up patrons that goes through pH testing and adjusting step-by-step.

To improve skin feel and reduce the chances of accidental over-application, I’ve included two thickening ingredients in this formulation: soft xanthan gum and polyquaternium 10 (which has a Humblebee & Me DIY Encyclopedia entry now!). They give the formula a rich, substantial feel that I really like. When you first mix everything up you will probably think “what the heck Marie? Why are we making face jelly?!”—but no worries! The viscosity drops to a much more, err, palatable level when we raise the pH of the formula. I wondered if this was soley due to the addition of the extra water in the NaOH solution so I tried a version where I added straight NaOH instead of the solution (which was a pain in the backside—I don’t recommend it!) and the viscosity still dropped.

Because acids have the potential to be irritating to the skin, I’ve included two skin-soothing ingredients: panthenol (vitamin B5) and allantoin. I was inspired to include some ingredients with anti-irritation properties by The Ordinary; their acid formulations include a Tasmanian pepperberry extract to head off potential irritation and sensitivity.

If you are new to including AHAs in your skincare routine, please start slow. I’d start with using this serum ~3x a week, gradually working up to daily use. Pay attention to your skin, looking for signs of irritation. More is not necessarily better!

As AHAs make your skin more sensitive to the sun, you must make sure you’re wearing a good sunscreen, even on days when you haven’t used the serum. This article from Lab Muffin mentions a study that found skin sensitivity took a week to return to normal after using a 10% glycolic acid product, so while I encourage daily sunscreen use regardless of AHA use, you’ll want to be extra diligent when you’re using AHAs and for a week afterwards if you stop using ’em. If you’re looking for a great sunscreen, I highly recommend checking out Japanese and Korean sunscreens. They are so much lighter than the sunscreens I’m used to buying in Canada, and they work a whole lot better to boot. Reddit’s Skincare Addiction has annual “holy grail” threads on sunscreen where you can find tons of recommendations. I really like the Biore UV Aqua Rich Watery Essence SPF40+ PA+++ 😄

Read this: Why Homemade Sunscreen is Never a Good Idea

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Relevant links & further reading

• Distilled water in the Humblebee & Me Encyclopedia
• Hyaluronic Acid in the Humblebee & Me Encyclopedia
• Ten Projects to Make with Hyaluronic Acid + hyaluronic acid Q&A
• Let’s Talk About Hyaluronic Acid
• Panthenol (Vitamin B5) in the Humblebee & Me Encyclopedia
• Allantoin in the Humblebee & Me Encyclopedia
• Propanediol 1,3 in the Humblebee & Me Encyclopedia
• Xanthan Gum in the Humblebee & Me Encyclopedia
• Polyquaternium 10 in the Humblebee & Me Encyclopedia
• Lactic acid in the Humblebee & Me Encyclopedia
• Liquid Germall™ Plus in the Humblebee & Me Encyclopedia
• Why Homemade Sunscreen is Never a Good Idea
• You’re Not Allowed to Have the Best Sunscreens in the World from The Atlantic
• How long will ______ last? What is its shelf life? in the Humblebee & Me FAQ
• Can I use a different preservative than the one you’ve used? in the Humblebee & Me FAQ
• pH
  • pH meter in the Humblebee & Me Encyclopedia
  • pH measurement in cosmetic lab: why we dilute samples? from Skin Chakra
  • How to adjust the pH of your cosmetic products from Skin Chakra
  • Why do you create a 10% dilution of a formulation before measuring the pH? in the Humblebee & Me FAQ
  • Amino Acids for pH Adjustment? from Realize Beauty (re: using L-Arginine for pH adjusting)
• More alpha hydroxy acid info:
  • Fact-check: Why Does pH Matter For AHAs And BHAs? from Lab Muffin
  • Do I Need Extra Sunscreen When Using Chemical Exfoliants? Fact-check Feature from Lab Muffin
  • Ingredient Spotlight: Hydroxy Acids from Stratia Skincare

5% Lactic Acid + Hyaluronic Acid Exfoliating Serum

61.35g | 61.35% distilled water
20g | 20% low molecular weight 1% hyaluronic acid solution (USA / Canada / New Zealand)
1g | 1% panthenol powder (vitamin B5) (USA / Canada)
0.4g | 0.4% allantoin (USA / Canada)

10g | 10% Propanediol 1,3 (USA / Canada)
0.2g | 0.2% xanthan gum (soft) (USA)
0.05g | 0.05% Polyquaternium-10 (USA / AUS)

5.55g | 5.55% 90% lactic acid solution (USA / Canada)
0.45g | 0.45% Liquid Germall Plus™ (USA / Canada)
1g | 1% NaOH (sodium hydroxide) 10% solution

Weigh the water, hyaluronic acid solution, panthenol, and allantoin into a beaker. Stir to combine, cover, and leave to dissolve.

While you’re waiting, stir the propanediol, soft xanthan gum, and Polyquaternium 10 together in a second beaker.

Add the lactic acid, Liquid Germall™ Plus, and NaOH solution to the water mixture. Stir.

Pour the water mixture into the gum mixture, and stir to combine. Cover the mixture and give the thickeners time to fully hydrate; you can speed this along by blending the mixture with a Mini Mixer.

Once the mixture is uniform, it’s time to test and adjust the pH.

To test and adjust the pH: create a 10% dilution by weighing 2g product and 18g distilled water into a small bowl or beaker and whisk to combine (wondering why we create a dilution to check the pH?). Check the pH with your pH meter. Depending on the shape of your bowl/beaker you may need to tilt it in order to fully submerge the sensor on your pH meter. We are aiming for a pH of 3.7–3.9; you will almost certainly need to raise the pH using more 10% NaOH solution, testing as you go. I have created a supplementary Patron exclusive video for this formulation that includes a step-by-step demonstration of making the 10% NaOH solution, testing the pH, and adjusting it; it’s available at $10 and up tiers. You can also read this article from Skin Chakra to learn more about pH adjusting.

When the pH of the solution is in the 3.7–3.9 range, package it up! Before you select a bottle, check the side of the beaker to see how much product you have left after pH testing and adjusting; you can end up losing a lot to testing as you get a feel for how much different amounts of the NaOH solution raise the pH. I divided my batch (I ended up with roughly as much as I started with) between three 30mL (1fl oz) clear bullet bottles fitted with orifice reducers (the orifice reducer + the viscosity from the thickeners means you can shake out a drop at a time). Other good options include bottles with treatment pump caps and dropper-top bottles.

If you are new to including AHAs in your skincare routine, please introduce this product to your routine slowly. I’d start with using a few drops of this serum ~3x a week, gradually working up to daily use. Avoid the eye area! I generally use this serum along with other watery serum type products, before any creams or oil serums. Pay attention to your skin, looking for signs of irritation, and discontinue/reduce use if your skin isn’t happy. Don’t forget your daily sunscreen!

Shelf Life & Storage

Because this serum contains water, you must include a broad-spectrum preservative to ward off microbial growth. This is non-optional. Even with a preservative, this project may eventually spoil as our kitchens are not sterile laboratories, so in the event you notice any change in colour, scent, or texture, chuck it out and make a fresh batch.

Substitutions

As always, be aware that making substitutions will change the final product. While these swaps won’t break the formulation, you will get a different final product than I did.

• As I’ve provided this formulation in percentages as well as grams you can easily calculate it to any size using a simple spreadsheet as I’ve explained in this post. As written in grams, this formulation will make 100g. This is quite a lot of product, but I wanted to be sure you had plenty for testing and adjusting the pH.
• To learn more about the ingredients used in this formulation, including why they’re included and what you can substitute them with, please visit the Humblebee & Me Encyclopedia. It doesn’t have everything in it yet, but there’s lots of good information there! If I have not given a specific substitution suggestion in this list please look up the ingredient in the encyclopedia before asking.
• You can replace the hyaluronic acid with more distilled water.
• You could try using a water-soluble botanical with skin soothing properties instead of (or in addition to) the panthenol (Vitamin B5) and/or allantoin. You may wish to use more; refer to supplier documentation for guidance, adjusting the distilled water to keep the formulation adding up to 100%.
• You could also leave the skin soothing ingredients out and replace them with more distilled water.
• You can use propylene glycol instead of propanediol 1,3.
• You can replace the Polyquaternium 10 with more soft xanthan gum; I’d probably use 0.3–0.4% soft xanthan gum as it’s not as potent of a thickener as Polyquaternium 10 is.
• You can try replacing the Polyquaternium 10 with 0.5% Polyquaternium 7, reducing the distilled water to make room for it.
• You could try replacing both (or either) of the thickening powders with a different powdered thickener like Hydroxyethylcellulose. Remember: different thickeners have different levels of potency/efficacy and different skin feels. Some are stickier than others, some are slimy. Changing the thickeners will change the feel of the formulation.
• You could also leave the thickeners out, replacing them with more distilled water. This will make for a very watery product, so make sure you package it accordingly.
• The lactic acid I used is 90% concentrated. If yours is 88% you’ll need to use 5.68% for an overall concentration of 5% lactic acid; adjust the distilled water to keep the formulation adding up to 100%.
• You could try making a serum like this with a different AHA; make sure you research it so you know which pH to aim for.
• If you’re like to use a different preservative, please review this FAQ and this chart.
• I’ve used 0.45% Liquid Germall™ Plus because my hyaluronic acid solution already contains it, and adds 0.05% to the overall formulation.
• To keep the irritation potential of this formulation as low as possible, I do not recommend adding an essential oil or fragrance oil to this formulation.