White Residue in Vitamin C Serum

Question

I am making a serum with the following formulation:

DI Water 45%
L-ascorbic acid 15%
Ethoxydiglycol 20%
Propylene Glycol 20%
AnyGel a little bit, enough to thicken

I mixed it in a brown plastic bottle and measured the pH to be 3-3.5. The first time I applied it, it was fine. But this time, after applying it for a while until the serum dries, it leaves a white powdery residue on the skin, like applying powder.

What could be causing this? What adjustments should I make?

MySkinRecipes Expert · Accepted Answer

Vitamin C Serum Residue Issue

The white, powdery residue you are seeing after the serum dries is likely caused by either:

Undissolved L-ascorbic acid: At 15%, L-ascorbic acid is a high concentration. If it doesn't fully dissolve in the liquid phase, the crystals can become visible as the serum dries on the skin.
Improperly hydrated thickener (AnyGel / Dehydroxanthan Gum): Gum thickeners need to be properly dispersed and hydrated. If not, ungelled particles can remain and leave a residue upon drying. This is a very common cause of this type of issue.

Recommendations:

Ensure L-ascorbic acid is fully dissolved: Add L-ascorbic acid to the water phase and stir until completely clear before adding other ingredients. Gentle warming of the water can help, but cool before adding other components.
Properly hydrate the thickener: This is crucial. Do not add the powder directly to the bulk liquid.
- Disperse the AnyGel in a small amount of Propylene Glycol or Ethoxydiglycol first to make a slurry, then add this slurry to the water phase while stirring vigorously.
- Alternatively, if adding directly to water, sprinkle the powder very slowly into the vortex of rapidly stirred water.
- After adding, stir well and let the mixture sit for 15-30 minutes to allow the gum to fully hydrate before continuing.
Check your mixing process: Since this issue is new, review your steps to see if anything changed, especially how you added the thickener.

Focusing on ensuring both the L-ascorbic acid is fully dissolved and the AnyGel is properly hydrated should resolve the white residue problem. The pH you measured is appropriate for the serum.