How long does hyaluronic acid filler stay, and how is it dissolved?

What is hyaluronic acid filler?

Hyaluronic acid is a water-binding molecule found naturally in the structure of the skin and connective tissue. The body's own hyaluronic acid is renewed within a few days; this is why the hyaluronic acid used as filler is turned into a gel through a process called “cross-linking”, so that it can remain in the tissue for longer. Cross-linked gel is more resistant than the natural molecule to enzymes and to the body's other breakdown pathways^[1].

How firm or soft the gel is, its particle structure and its density differ between products. These properties affect both how the gel behaves in the tissue and how long its effect is maintained^[2].

Why does filler break down over time?

The injected gel is gradually broken into small fragments by hyaluronidase enzymes in the tissue and by oxidative processes; these fragments are then cleared by the body^[1]. This happens gradually rather than all at once. A fading visible effect is not the same as the gel having disappeared from the tissue completely: imaging studies show that small amounts of gel may still be present in the tissue even when the effect has faded^[3].

Factors that affect how long it stays

The effect of hyaluronic acid filler can range from a few months to more than a year on average; this varies from person to person, and it would not be right to give a precise figure in advance. The main factors that determine how long it stays are^[2][3]:

• Area: In constantly moving areas such as the lips, the gel may break down faster; in less mobile, deeper areas it tends to stay longer.
• Product structure: The degree of cross-linking and the density of the gel affect duration. Which product is used is chosen by the doctor according to the area and the aim.
• Amount and injection depth: The amount is determined in ml at the examination; the tissue layer in which the gel is placed also changes how long it stays.
• Individual factors: Metabolism, skin structure, sun exposure and lifestyle habits differ from person to person.

Dissolving filler with hyaluronidase

Hyaluronidase is an enzyme that breaks down hyaluronic acid. One of the most important features of hyaluronic acid filler is that it can be dissolved with this enzyme if needed^[4]. Dissolving may be considered in the following situations:

• The filler spreading to a different place than expected, or an irregular appearance,
• Swelling or firmness (a nodule) at the injection site that does not go away for a long time,
• Situations requiring urgent intervention, such as suspected vascular occlusion (a blocked blood vessel)^[5],
• The person wishing to have the filler removed after discussing it with their doctor.

The decision to dissolve is made by the doctor after an examination. The enzyme is also given by injection; brief redness, swelling or bruising may appear afterwards. Because an allergic reaction can develop, although rarely, you will be asked about allergies before the treatment^[4]. In some cases a single session may not be enough, and reassessment at the follow-up may be needed.

How is a repeat treatment planned?

When the effect of the filler fades, whether to repeat the treatment, when and with how much is assessed at the examination. This assessment takes into account whether gel is still present in the area, the condition of the tissue and the response to previous treatments. Because repeated treatments while a small amount of gel remains in the tissue can, over time, lead to unwanted fullness in the area, planning is done with caution^[3].

If you have had filler elsewhere before, mention at the examination, if possible, when it was done, in which area and what type of product was used. If a substance other than hyaluronic acid was used, hyaluronidase will not dissolve that filler; this information matters for planning. If you don't know, that's fine too; your doctor will make an assessment based on the examination findings.

Possible side effects and late reactions

Redness, swelling and bruising may appear after a filler treatment; these usually decrease within a few days. Most fillers contain a local anaesthetic; a topical anaesthetic cream is applied for about 30 minutes before the treatment. The treatment takes 10–20 minutes on average, and you can wash your face half an hour afterwards. After treatment at the angle of the jaw, you may feel pain when chewing for 1–2 days.

Less often, swelling, redness or firmness may appear at the injection site weeks or months after the treatment. Consensus reports state that hyaluronidase is an important option in assessing and managing these late reactions^[6]. If you notice anything like this, contact your doctor rather than treating it yourself.

A follow-up visit takes place within 1 month of the treatment. Filler treatment is not carried out during pregnancy or breastfeeding.

Further reading

• Dermal fillers and facial contouring
• Lip filler: what you need to know before and after
• Botox or filler? The differences
• Under-eye dark circles and hollows
• Preparing for an aesthetic treatment