Hyaluronic acid: what does "reversible" mean?

A gel close to a molecule of the skin

Hyaluronic acid is a molecule naturally present in the skin, where it holds water. For it to last several months once injected, its chains are linked together: this is called a crosslinked gel. Most products use a small molecule for this, BDDE, of which only tiny traces remain in the finished product.

In Europe, these gels are implantable medical devices in the highest risk class, class III. Their name, the quantity injected and their batch number are recorded in your file: the exact product can be traced at any time.

Reversible, thanks to an enzyme

Hyaluronidase is an enzyme that breaks down hyaluronic acid. Injected in the right place, it dissolves the gel. It can correct a small irregularity or an excess, and above all quickly treat a rare complication: a blood vessel blocked by the product.

This complication is rare. In a large survey of dermatologists, it occurred about once per 6,400 syringes injected with a needle, and much less often with a cannula. Guidelines call for treating it without delay, with repeated injections of hyaluronidase. This is why hyaluronidase is always available at the practice.

What "reversible" does not mean

• That the product disappears quickly. MRI scans show that hyaluronic acid can remain much longer than the announced duration, sometimes several years.
• That one can inject without thinking, since it can always be dissolved. Hyaluronidase has its own risks, including rare allergic reactions, more frequent in people allergic to wasp or bee stings.
• That all fillers are reversible. Products based on calcium hydroxylapatite, poly-L-lactic acid or polycaprolactone are not dissolved by hyaluronidase. At the practice, the fillers used are hyaluronic acids.

What it changes in my practice

Reversibility is a safety net, not an excuse. It makes it possible to proceed in small amounts, to measure, then to stop. Before a treatment, I ask you, among other things, whether you are allergic to insect stings. The name of the product, its quantity and its batch number appear in the written report you sign, as Belgian law requires.