What are the various modes of application for hyaluronic acid?

On the skin, hyaluronic acid is initially used for its powerful hydrating properties. Able to retain up to 1,000 times its weight in water, it helps maintain hydration of the epidermis, strengthens the barrier function and improves skin suppleness. hyaluronic acid exists in different molecular weights. The high molecular weight form creates a protective film on the skin’s surface, while the low molecular weight form penetrates deeper into the epidermis and helps reactivate cellular activity. Topical application of hyaluronic acid can therefore enhance skin radiance and smooth dehydration lines. Moreover, studies have shown that hyaluronic acid possesses anti-inflammatory, antioxidant and healing properties, demonstrating its versatility.

The application of skincare products containing hyaluronic acid can be applied morning and evening, since this active ingredient is not photosensitising. It is found in serums, creams or lotions, at concentrations varying but often between 0.01% and 3%. Hyaluronic acid can be used alone or in conjunction with other active ingredients, such as vitamin C or niacinamide, which are also very popular in cosmetics. It presents no particular contraindications and is well tolerated by all skin types, including the most sensitive. Hyaluronic acid is also compatible with skincare products containing retinoids or fruit acids, as a complement to limit irritation.

As far as hair is concerned, the scientific data are more limited, but hyaluronic acid appears promising, notably for enhancing the strength of the hair fibre. On the scalp, its effects are similar to those observed on the skin, where hyaluronic acid can soothe irritations and improve hydration and the skin barrier. The hyaluronic acid can be found in shampoos, conditioners, masks or hair serums. Its mode of application depends on the type of formulation: some products require a leave-on time, others are applied as leave-in treatments. It is recommended to follow the manufacturer’s instructions. Finally, it is useful to know that hyaluronic acid is considered an active ingredient suitable for all hair types, whether coily, straight, curly or dull.

The hyaluronic acid is also highly prevalent in the field of aesthetic medicine. Unlike topical hyaluronic acid, injections can act in depth to fill pronounced wrinkles, restore facial volume, redefine contours, plump the lips or even reduce certain scars. However, these medical procedures are strictly contraindicated in pregnant or breastfeeding women, patients with autoimmune disorders, those on anticoagulant therapy or presenting with a skin infection. It is also recommended to avoid any sun exposure in the days leading up to the session.

Did you know? The hyaluronic acid used in injections is generally cross-linked hyaluronic acid, a specific form created by chemically linking multiple chains with a cross-linking agent to form a dense three-dimensional structure that is less prone to enzymatic breakdown in the skin.

Hyaluronic acid injections are performed using a blunt-tipped cannula, directly into the dermis. The procedure, typically mildly painful, may produce a tingling sensation during injection, which is alleviated by the prior application of a local anaesthetic. Depending on the area to be treated, the session lasts between 10 and 30 minutes. Results generally become visible between one and four weeks after the procedure and persist on average between 6 and 24 months, depending on the density of the injected gel and its location. Due to the inflammatory response induced by the injection, it is advisable to avoid any sun exposure for the week following treatment. Although adverse effects associated with hyaluronic acid injections are relatively rare, they should not be overlooked: redness, bruising, swelling, and, in more severe cases, bacterial infections or localised necrosis may occur. Careful medical follow-up helps prevent most complications and allows for prompt management.

Oral supplementation with hyaluronic acid is attracting growing interest, yet its true effects remain to be confirmed.

Some studies suggest that a daily intake of hyaluronic acid could help enhance skin hydration, improve skin suppleness, and even strengthen joint function. A 2016 publication by OE and their team reviewed the existing scientific literature on this subject and concluded that oral hyaluronic acid might emerge in the future as an interesting complementary solution for joint pain. This active compound could modulate inflammation by upregulating cytokine signalling-3 expression and downregulating pleiotrophin expression via the Toll-like receptor 4 in intestinal epithelial cells.

Studies investigating the effects of hyaluronic acid on the skin are still limited in number and often funded by industry stakeholders, which calls for caution when interpreting the results. Moreover, once ingested, hyaluronic acid is hydrolysed in the digestive system, particularly in the stomach and intestine. It remains unclear where precisely these fragments accumulate in the body. There is no evidence to suggest that they are preferentially directed to the skin, a peripheral organ that the body does not regard as a vital priority. With current knowledge, it is therefore premature to conclude that dietary supplements containing hyaluronic acid significantly improve skin hydration or elasticity.

Hyaluronic acid–based dietary supplements are typically supplied as capsules or pills. Depending on the formulation, the recommended dosage ranges from 100 to 300 mg per day, sometimes in combination with other active ingredients such as collagen or zinc. Manufacturers often recommend a single daily dose, preferably taken with meals. The duration of supplementation varies according to the desired outcomes, but a 1 to 3-month period is generally advised to evaluate any potential effects. To date, no adverse reactions have been reported following oral hyaluronic acid supplementation, although it is usually not recommended for pregnant women as a precautionary measure. Furthermore, as with any dietary supplement, it is advisable to consult a healthcare professional before commencing supplementation, particularly in cases of chronic illness or when taking other medications.

Hyaluronic acid is commonly used in rheumatology to relieve pain associated with osteoarthritis, particularly in the knee. Naturally present in synovial fluid, it contributes to the lubrication and shock absorption of the joints. In osteoarthritis, its concentration and viscosity decrease, reducing cartilage protection and promoting painful joint friction. Intra-articular injection of hyaluronic acid, a procedure also known as viscosupplementation, aims to restore the viscoelastic properties of synovial fluid. Several studies have shown a moderate improvement in pain and mobility, especially in mild to moderate knee osteoarthritis. However, efficacy remains variable between individuals and the observed benefits tend to diminish as joint damage becomes more severe. Moreover, the relief is not immediate: it generally appears within a few weeks after injection and lasts only a few months.

The hyaluronic acid used in this context is injected directly into the joint by a healthcare professional, most often under ultrasound guidance. One to three injections may be offered, at weekly intervals depending on the product. Although this procedure is minimally invasive, it is not without risk. Local adverse effects can occur, such as transient pain, swelling or joint inflammation. Infections are rare but possible. Hyaluronic acid injections are generally well tolerated and represent an attractive option when first-line treatments, such as analgesics or physiotherapy, prove insufficient. However, they are not recommended in cases of joint infection or acute inflammatory flare-ups. Their efficacy in joints other than the knee—such as the hip, shoulder or ankle—remains debated within the medical community.

Hyaluronic acid is also used in eye drops to relieve the symptoms of dry eye. Naturally present in the connective tissues of the eye, it retains water there and contributes to the maintenance of ocular moisture and to the stabilisation of the tear film. However, the eyes can nevertheless become dry, and the hyaluronic acid naturally present may no longer be sufficient to keep them hydrated. This can notably be due to certain autoimmune conditions, such as Sjögren’s syndrome, to the use of medications such as antihistamines or isotretinoin, an oral retinoid used in the treatment of acne, or indeed to dry air, the continuous wear of contact lenses, or prolonged exposure to screens.

Hyaluronic acid–based eye drops are available over the counter and can be used several times a day, with no real restriction, as required. Their concentrations generally range from 0.1% to 0.4%, with the most highly concentrated formulations often reserved for moderate to severe ocular dryness. Some products contain only hyaluronic acid, while others include complementary moisturising and soothing agents, such as trehalose or the allantoin.

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