Injectable filler

Injectable filler is a substance made to be injected into connective tissues, such as skin, cartilage or even bone, for cosmetic or medical purposes. The most common application of injectable fillers is to change one's facial appearance, but they also are used to reduce symptoms of osteoarthritis, treat tendon or ligament injuries, support bone and gum regeneration, and for other medical applications. Injectable fillers can be in the form of hydrogel or gels made from pulverized grafts.

Injectable fillers have risen in popularity mostly due to the wide application of dermal fillers in 1980s. Their premise is to help fill in facial wrinkles, provide facial volume, and augment facial features. Side effects include bruising or infections from improper sterilisation. This may include HIV infection, also allergic reactions, which may cause scarring and lumps. Blindness due to retrograde (opposite the direction of normal blood flow) embolization into the ophthalmic and retinal arteries can occur.

Injection of dermal fillers is the second most common nonsurgical cosmetic procedure in the United States, used for addressing volume deficiency, scars, wrinkles, and enhancing facial features and specific anatomical sites like the lips. There is a continued increase in the variety of available dermal fillers.[1]

Materials used

Injectable fillers are composed of a wide range of natural and synthetic biomaterials, which can be categorized as resorbable or non-resorbable polymers. Injectable fillers are frequently formulated as hydrogels composed of hydrophilic polymer networks that can retain large amounts of water while maintaining structural integrity.[2] Common materials include naturally derived polymers such as hyaluronic acid, Gelatin, collagen, Chitosan, alginate, and polysaccharides, as well as synthetic polymers like polyethylene glycol (PEG), poly(lactic acid), poly(methyl methacrylate), polyacrylamide, and dextran.[3][2] These materials are often selected for their biocompatibility and structural similarity to the extracellular matrix, enabling integration with surrounding tissues.[2] To enable in situ gelation, polymers are typically functionalized with reactive groups such as phenols, amines, or glutamine residues, allowing controlled crosslinking

Medical uses

Injectable fillers are widely used in cosmetics for soft tissue augmentation and facial rejuvenation. Their primary clinical applications include the correction of facial wrinkles and folds, restoration of age-related volume loss, and the enhancement of facial contours such as the lips, cheeks, and jawline.[3] Hyaluronic acid-based fillers are commonly used for superficial and mid-dermal injections to treat fine lines and improve skin hydration, while more robust fillers are injected into deeper tissue layers to correct severe wrinkles and provide structural support. Biodegradable fillers, such as poly(lactic acid), can stimulate collagen production, contributing to longer-term volume effects.[3]

Injectable hydrogel-based fillers have been investigated for a wide range of medical applications due to their biocompatibility, injectability, and ability to form three-dimensional networks in situ. In wound healing, these materials provide a moist environment, act as barriers against infection, and conform to irregular tissue defects, thereby promoting tissue regeneration.[2] They are also used to prevent post-operative adhesions by acting as physical barriers that separate tissues during healing, reducing fibrotic attachment.[2]

Pharmacokinetics

Most wrinkle fillers are temporary because they are eventually metabolized by the body. Some people may need more than one injection to achieve the wrinkle-smoothing effect. The effect lasts for about six months. Results depend on health of the skin, skill of the health care provider, and the type of filler used. Regardless of material (whether synthetic or organic) filler duration is highly dependent on amount of activity in the body area where it is injected. Exercise and high intensity activities such as manual labor can stimulate blood flow and shorten the lifespan of fillers.[12]

Side effects and risks

Risks of an improperly performed dermal filler procedure commonly include bruising, redness, pain, or itching. Less commonly, there may be infections or allergic reactions, which may cause scarring and lumps that may require surgical correction.[13] In 2024, a cluster of HIV infections was described amongst clients receiving microneedling facials at a spa.[14] More rarely, serious adverse effects such as blindness due to retrograde (opposite the direction of normal blood flow) embolization into the ophthalmic and retinal arteries can occur.[15] Delayed skin necrosis can also occur as a complication of embolization.[16] Embolic complications are more frequently seen when autologous fat is used as a filler, followed by hyaluronic acid. Though rare, when vision loss does occur, it is usually permanent.[17]

Society and culture

In the US, fillers are approved as medical devices by the Food and Drug Administration (FDA) and the injection is prescribed and performed by a provider. What defines a qualified dermal injection provider varies by country and is a point of debate between board-certified doctors and injectors who operate under cosmetic or aesthetician licenses.

Fillers are not to be confused with neurotoxins such as Botox. Fillers are not approved for certain parts of the body where they can be unsafe, including the penis.[18] In the European Economic Area and the UK, fillers are non-prescription medical devices that can be injected by anyone licensed to do so by the respective medical authorities. They require a CE mark, which regulates adherence to production standards, but does not require any demonstration of medical efficacy. As a result, there are over 140 injectable fillers in the UK/European market and only six approved for use in the US.[19]

In China, the NMPA (formerly CFDA) has also issued guidance to regulate injectable fillers.[20]

See also

• Cosmetic surgery