This Bi-Phase Hyaluronic Acid Hair Serum is part leave-in hair conditioner, part hair serum. It features hydrating and luxurious hyaluronic acid, volume-boosting hydrolyzed rice protein, and ultra-light Neossance® Hemisqualane—I am loving working a few pumps through my hair from about the ears down. My ends are pretty dry these days as I am well overdue for a trim, but this serum perks it right up! And, since it’s a bi-phase serum it’s incredibly simple to make while still getting the benefit of both oil and water-soluble ingredients. Let’s dive in!

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I first learned about bi-phase formulation in my Formula Botanica coursework. A bi-phase formulation takes something we’d usually consider a failure—separation—and turns it into a key feature of the formulation. It’s not a super common formulation style, but you can definitely find bi-phase products for sale if you go looking; many of the ones I’ve found are makeup removers, but you can find other formulations like serums and salt sprays as well.

The biggest benefit of a bi-phase formulation is pretty obvious; since we aren’t worried about separation, we don’t have to fuss with emulsifiers or the stability of the emulsion. We still get the diluting impact of mixing water and oil, it’s just easier. Since the product isn’t emulsified it remains quite thin, and you’ll want to make sure you aren’t using oil phase ingredients that’ll thicken up so much that they won’t incorporate well when the product is shaken before use (imagine a lump of shea butter shaken in a jar of water—you’ll just have a lump of shea butter floating around in the water). This required thinness makes bi-phase formulations best suited for serum-y type things.

Since my hair only needs a wee bit of oil, the oil phase of this serum is quite small. It’s primarily comprised of two lightweight emollients; Neossance® Hemisqualane and camellia seed oil, at 5% each. If you wanted to make this serum even lighter you could swap the Neossance® Hemisqualane for some cyclomethicone, or simply reduce the amount of either or both of the emollients (making up for the loss with more distilled water). If you’d like to make the serum richer, simply use more oil, dialling back the water to make room for it.

The water phase stars hyaluronic acid to help hydrate and moisturize the hair. You’ll also find some richly conditioning polyquaternium 7, volumizing hydrolyzed rice protein, and shine-boosting panthenol. The hydrolyzed rice protein is brown, so the entire water phase takes on a pale golden-y colour that contrasts a bit with the clear oil phase floating on top.

I tried packaging this formulation in both a mister-top bottle and a treatment pump bottle. Both work, but you won’t really get the misty benefits of the mister top bottle as this formulation is just a wee bit too thick to mist. It dispenses, but in more of a concentrated blast—concentrated enough that I couldn’t apply it straight to my hair without getting a greasy spot, so I ended up spritzing it into my hand and then working the product through my hair with my fingers. Whatever you use, make sure you shake well before use.

Relevant links & further reading

• Hyaluronic Acid in the Humblebee & Me Encyclopedia
• Polyquaternium 7 in the Humblebee & Me Encyclopedia
• Hydrolyzed Rice Protein in the Humblebee & Me Encyclopedia
• Liquid Germall Plus in the Humblebee & Me Encyclopedia
• Panthenol (Vitamin B5) in the Humblebee & Me Encyclopedia
• Neossance® Hemisqualane in the Humblebee & Me Encyclopedia
• Camellia Seed Oil in the Humblebee & Me Encyclopedia
• Tocopherol (Vitamin E) in the Humblebee & Me Encyclopedia
• Can I use a different preservative than the one you’ve used? in the Humblebee & Me FAQ
• Preservatives + Shelf Life in the Humblebee & Me FAQ
• Other leave-in hair formulations:
  • Dry Argan Oil Hair Mist
  • Rose & Tea Ultra-Light Conditioning Hair Balm
  • Silk & Camellia Seed Leave-In Hair Conditioner
  • Argan Rose Conditioning Hair Balm
  • Summer Shimmer Hair Oil

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Bi-Phase Hyaluronic Acid Hair Serum

Water phase
32.35g | 64.7% distilled water
10g | 20% low molecular weight 1% hyaluronic acid solution (USA / Canada / New Zealand)
0.5g | 1% Polyquaternium 7 (USA / Canada)
1.5g | 3% hydrolyzed rice protein (USA / Canada)
0.25g | 0.5% Liquid Germall Plus™ (USA / Canada)
0.25g | 0.5% panthenol powder (vitamin B5) (USA / Canada)

Oil phase
2.5g | 5% Neossance® Hemisqualane (USA / Canada)
2.5g | 5% camellia seed oil
0.05g | 0.1% fragrance oil or essential oil of choice
0.1g | 0.2% Vitamin E MT-50 (USA / Canada)

Weigh all the ingredients into a small beaker, or directly into the bottle you’ll be storing the serum in.

If it’s a beaker, stir to combine. If you went straight for the bottle, cap and shake.

For packaging: I recommend something with a treatment pump cap for dispensing, though a mister will work. Please watch the video for more details. This isn’t the prettiest serum to look at, so I’d choose a frosted, tinted, or opaque bottle rather than a clear one 😂 I used a Zelo frosted bottle from New Directions; the cap I used has been discontinuied, but they do have other dispensing pump caps that would be suitable.

That’s it!

To use, shake to combine before dispensing into your palm. Work through your hair—I prefer to apply this from the ears down, but definitely experiment and see what works for you. Enjoy!

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 recipe, you will get a different final product than I did.

• As I’ve provided this recipe 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 recipe will make 50g, which will fill a 50mL (1.69fl oz) bottle nicely.
• 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 (panthenol, vitamin E) please look up the ingredient in the encyclopedia before asking.
• If you don’t have the hyaluronic acid I’d replace that 20% with 5% glycerine and 15% distilled water.
• You could try a different water soluble conditioning ingredient instead of Polyquaternium 7, like honeyquat or polyquaternium 10. Make sure you’re checking usage rates for whatever you use to ensure you’re using a suitable amount. I don’t recommend using a solid fatty conditioner like behentrimonium chloride (BTMC) or BTMS.
• You can replace hydrolyzed rice protein with a different hydrolyzed protein (oat, baobab, quinoa, etc.).
• If you’re like to use a different preservative, please review this FAQ and this chart.
• You can substitute another lightweight oil like sweet almond, grapeseed, or sunflower seed for the camellia seed oil. You could also choose a different luxury oil that your hair loves, like Argan Oil.
• Make sure whatever fragrance oil or essential oil you use is safe to use in leave-on products at 0.1%; most will be, but always double-check!