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Hyaluronic acid is a white, fibrous or powdered solid that is odourless and tasteless. It has strong hygroscopic and moisturising properties, and dissolves slowly and completely in water. One gram of hyaluronic acid can absorb up to 1,000 times its weight in water to form a slightly milky white or colourless viscous solution. It is therefore widely used in the cosmetics, medical aesthetics and plastic surgery industries. What many people don’t know is that the human body naturally produces hyaluronic acid, particularly in areas such as the eyes, joints and skin.

In the medical beauty industry, hyaluronic acid injection is the most common treatment method. It hydrates and moisturises the skin and can fill skin depressions. However, if injected excessively, at improper levels or with non-standard products, it can cause local nodules, swelling and vascular compression. Retention in the body over a long period of time may also cause inflammatory reactions or granulomas.

Over time, the body gradually absorbs or excretes the hyaluronic acid, achieving its repairing effect. Due to variations in body constitution, the rate of hyaluronic acid excretion can differ from person to person. But how long does hyaluronic acid remain in the body? A study published in the Plastic and Reconstructive Surgery journal may surprise you: the article states that, once injected, hyaluronic acid can remain in the body for up to 12 years. This article summarises the findings of the study.

This study collected data from 14 patients who had received hyaluronic acid injections at various times. Magnetic resonance imaging (MRI) was used to examine the location, distribution and retention duration of the hyaluronic acid in the patients’ bodies, as well as any adverse reactions.

The results showed that ten people reported not having received hyaluronic acid facial injections within two years before the MRI examination. However, the imaging examination results showed residual hyaluronic acid signals. Five of these people reported not having received hyaluronic acid injections within six years before the MRI examination. Again, the imaging examination results showed hyaluronic acid signals. One person reported not receiving periorbital hyaluronic acid injections for 12 years prior to the MRI examination; however, the imaging results revealed hyaluronic acid signals in the patient’s periorbital area. This proves that hyaluronic acid can remain in the body for up to 12 years.

Now, let’s take a look at a case study.

Case 1: A 54-year-old female patient had received hyaluronic acid injections in her lips, tear troughs and cheeks. She reported not having received any injections in the two years prior to the examination. Imaging results revealed the presence of hyaluronic acid in the lips, tear troughs and cheeks. The hyaluronic acid found in the upper lip mucosa (above the orbicularis oris muscle) may have been injected incorrectly or has migrated since the procedure.

Case 2: A 37-year-old female patient reported receiving large-dose hyaluronic acid injections in her nasolabial folds six years ago. Imaging results revealed hyaluronic acid deposits deep within the nasolabial folds.

Case 3: A 52-year-old female patient reported receiving a hyaluronic acid injection into the buccal fat pad two years ago, at a dose of around 3 ml. Imaging revealed hyaluronic acid signals deep within the buccal fat pad, positioned above the periosteum.

While most patients who receive hyaluronic acid injections for medical aesthetics understand their effects, they are often unaware of the common risks that remain afterwards. The main risks are:

Compression and deformation of body tissues – Excessive or deep residual hyaluronic acid can put pressure on blood vessels and nerves, resulting in numbness of the skin due to local ischaemia. Improper superficial injection can create uneven lumps that affect the natural appearance of the face.

Delayed inflammation and immune response – Some people are sensitive to hyaluronic acid, but this sensitivity may not become apparent until several months after the injection. Instead, redness, itching or the formation of granulomas may occur several months later. This allergic reaction requires medication or dissolving enzymes to treat it.

Embolism risk – if residual material enters a blood vessel, it can cause an embolism, which may manifest as blanching and pain. If injected around the eye, it can result in vision loss and require immediate medical attention. Although this risk is rare, the consequences can be very serious if it occurs.

Currently, MRI scanning is an effective tool for examining the location, migration and retention of hyaluronic acid in the body. This study showed that residual hyaluronic acid persisted in patients 12 years after injection; however, the cause of this residue remains unclear. These findings serve as a reminder for physicians and patients to strengthen postoperative follow-up and self-management after hyaluronic acid injections. Despite the small sample size, the majority of patients being unaware of the circumstances surrounding the injections and the relevant product information, injection level and method being unknown, the findings still provide valuable insights for patients who received the injections.

Some patients who have received injections may be confused by this conclusion because their doctor must have told them that the injection would only last for three to six months or one year, and that they would need to receive another injection once the time was up. Here, we must mention the concept of concentration. Hyaluronic acid can be divided into three categories based on its concentration: low, medium and high. The low concentration standard is below 0.2%. It has a thin texture, good fluidity and is quickly absorbed. Put simply, it is similar to water and is often used in everyday cosmetics. The medium concentration standard is between 0.5% and 2%. It has a gel-like consistency, similar to jelly, and provides slight support. It is most commonly used in medical beauty treatments, such as hydration injections. The high concentration standard is greater than 2%. Hyaluronic acid needs to be cross-linked to form a solid gel that provides strong support and is not easily degraded. This makes it the best choice for filling, shaping and lifting. However, remember that it is non-degradable.