Hyaluronic acid concentration in mg/ml: what it tells you

The concentration of hyaluronic acid is the amount of HA in each milliliter of the product, expressed in milligrams per milliliter (mg/ml). It is the number that appears on the packaging and the technical data sheet of fillers and injectable hydration products. It tells you how much material is in the gel, but on its own it does not say whether the product is firm, soft, more or less durable, or for which area it is suited.

What goes into this number?

In most fillers, the declared concentration is that of total HA, which adds up two fractions:

The ratio between the two fractions changes from one product to another and does not always appear on the labeling. That is why two gels with the same total concentration can have quite different amounts of structural HA.

Does a higher concentration mean a firmer gel?

Not necessarily. Firmness, measured by G prime, depends on concentration, but also on the degree and type of crosslinking, the molecular weight of the chains, the particle size and how the gel is prepared. A gel with fewer mg/ml and denser crosslinking can be firmer than another with more mg/ml and light crosslinking.

The same goes for duration. The breakdown of the gel in the tissue depends on the structure that crosslinking creates, and not only on the amount of HA. Comparing products by concentration alone leads to wrong conclusions. The combined reading of the properties is in rheology and in cohesivity.

So what is the point of looking at concentration?

It is still useful in three ways:

• Water uptake: HA attracts water, and a more concentrated gel may have a greater tendency to gain volume in the first few days, depending on the hydration state at which it was manufactured. The topic is covered in hyaluronic acid hydrophilicity.
• Total mass injected: multiplying the concentration by the volume gives the amount of HA that stays in the tissue.
• Product class: injectable hydration products, such as skinboosters, usually have a different profile from volumizing fillers, and concentration helps place the product.

Hypothetical example: a 1 ml syringe of a 20 mg/ml gel delivers about 20 mg of HA to the tissue; 0.5 ml of the same gel delivers about 10 mg. This calculation says nothing about firmness or duration, only about quantity.

How does this show up in practice?

In the consultation, concentration matters more in choosing the product than in the conversation with the patient. It can help explain why a gel swells more in the first few days or why two products from the same manufacturer have different indications. The view by area is in hyaluronic acid by area, and the difference between crosslinked and free gel is in crosslinked and non-crosslinked hyaluronic acid.

Also called: HA concentration, hyaluronic acid content, filler mg/ml.