Dr Ahmed El-Houssieny explores how microinjections of hyaluronic acid fillers can boost skin quality
When a patient presents with skin characterised by fine wrinkles, reduced elasticity, or that is dry or rough, one treatment to consider is the application of a skin booster. The injection of small doses of a fine hyaluronic acid (HA) filler into the dermis can give a universal improvement in skin quality by maintaining skin hydration and reducing signs of ageing, without adding volume or lift.1
However, using HA fillers as a skin booster is quite distinct from its use in other more targeted treatments.2,3 As practitioners, it is important to ensure that we are familiar with the science, suitable products, application techniques and patient selection for skin boosting treatment so that we can offer this holistic approach to firmer, tighter skin.
Around half of the body’s HA is found in the skin and is produced by both fibroblasts and keratinocytes.2 HA is a non-sulfated glycosaminoglycan that is found in high levels in the dermis, epidermis and extracellular matrix (ECM).2,4 Structurally, it is a simple linear polymer which contains many repetitions of a disaccharide, creating a large hydrophilic molecule. In fact, HA can hold water molecules up to 1,000 times its weight.5
Levels of HA decrease in ageing skin and along with fragmentation of the ECM, disorganisation of dermal elastic fibres and reduced collagen production, this can result in loss of elasticity, the appearance of fine lines, thinning skin and dryness.2,3 HA fillers use the hydrating properties of HA to restore turgor and improve texture and elasticity to the skin.1,2,4 The hydrophilic properties of HA mean that when injected into the dermis, HA introduces tension into the extracellular matrix, which stretches protein fibres and stimulates fibroblasts which in turn may stimulate increased collagen production.2,6 The clinical manifestation of this is softer and firmer skin.1
Many dermal fillers are inserted beneath the skin in the fat layers, supraperiosteal layer or even the retaining ligaments to treat deeper wrinkles, add volume, lift or to contour.1,2,7 Others are injected into the dermis.2,7 Of these, some are injected in a targeted way to treat fine lines or wrinkles while those that HA fillers used to give a universal boost to the skin are injected across a larger area using a series of micropunctures.1,2 Not only Is the application different when administering a universal skin boost, but specific products should be used which have developed for the purpose.1-3 There are several available in the UK including: Belotero Revive, Juvéderm, Profhilo, Restylane Vital and Vital Light and Teosyal Puresense Redensity.1,2,8-11 It should be noted that the Restylane products have the brand name SkinBoosters but the other products listed here are also designed to boost the skin. Skin boosting products differ in terms of the level at which they are injected in the dermis and details should be checked for each product prior to use.1
One of the key differences between skin boosting injectable products and other HA fillers is the degree to which they are cross-linked. A cross-linked structure is formed by binding together two chains of HA, commonly using the molecule 1.4-butanediol diglycidyl ether (BDDE).1 This creates a three-dimensional network which results in a firm gel that retains its shape.1 The greater the level of cross-linking, the denser and firmer the gel.1 Unlike other HA injectables, those developed as skin boosters either have very low levels of cross-linking or are not cross-linked at all.2
Elasticity is determined by cross-linking and skin boosting fillers that have no or few cross-links have low elasticity.2,12 However, skin boosting fillers have been shown to restore some elasticity to the skin which may be due to the stimulation of collagen production by the HA itself.1,13 While cross-linking is the main determinant of the mechanical properties of any given filler, HA concentration and particle size also play a key role.2,7,14,15
During the manufacturing process, the cross-linked or non-cross-linked gel is further refined to produce a filler with properties appropriate to its intended use.15,16 The cohesivity of fillers, the internal adhesion between the filler particles, depends on HA concentration as well as the degree and type of cross-linking. Although the degree of HA concentration varies between products, skin boosting fillers are manufactured to have low cohesivity.1,3 They also have low viscosity.1,2 Viscosity is determined by the size and weight of the HA particles and particle size tends to be small in this type of filler.1,12
These properties are suited to the way in which skin boosting fillers are used.1,2,17 Due to their superficial injection, skin boosters are required to be softer and smoother than a filler that is injected more deeply.2 They also require the capacity to be moulded so that an even spread can be achieved and the formation of any lumps avoided.2,17 Smaller particles can retain more water than larger particles and can hydrate the skin without adding significant volume.1,18 Small particle skin boosting HA fillers have been shown to be effective in hydrating the skin of the face, neck and hands.17
Cross-linking in HA fillers also has a stabilising effect and improves longevity; HA that has not been cross-linked is reported to last for a shorter period than cross-linked HA fillers, with a half-life of a few weeks after injection.1,12 However, some skin boosting HA fillers have a degree of cross-linking while others improve the duration of their hydrating effect through the inclusion of a polysaccharide such as glycerol or mannitol.1
Skin boosters can be used on all areas of the face, including the chin and periocular areas as well as on the neck, décolletage, hands, arms and knees.1 A pre-treatment photograph is a useful way of demonstrating the results of skin boosting treatment to the patient over time, and should be taken before treatment commences.
A plan of application should be drawn up with uniformly distributed injection points that cover the whole area to be treated.1 Small aliquots of product are administered: approximately 0.02ml per puncture has been used effectively in facial injections.1,13 Maximal volumes of 0.5ml per cheek, 0.3ml for each side of the neck, and 0.5ml for each hand were used effectively in another study of 20 subjects using the same product.17 Another author suggests levels of 1ml per cheek, and 1-2ml for the forehead or neck with a different filler product.19 The product dosing information should be checked prior to injection. These amounts may differ between products and product dosing information should be checked prior to injection.
Cannula use is an option with stabilised fillers and can be used in all facial areas but is particularly useful where the skin is very thin, such as in the periorbital area
HA fillers for boosting skin are designed to be injected into the dermis.2 Non-cross-linked (also called non-stabilised) fillers should be injected in the superficial dermis, whereas those with low cross-linking (stabilised) into the mid- or deep dermis.1 There are further differences in approach between stabilised and non-stabilised fillers.1 For non-stabilised HA fillers, injection into the superficial dermis with a needle is recommended and should be administered as a series of punctures.1 This should leave translucent micropapules on the surface of the skin (Figure 1). These are part of the treatment process and will settle after five to seven days.1 With stabilised fillers, the appearance of such papules is considered a side effect and should be avoided by ensuring the filler is injected deeper in the dermis.1,19
With cross-linked skin boosters, the practitioner has a choice of serial punctures or retroinjection with the latter reported to be safer, easier to control and to avoid the risk of papule formation.1 Cannula use is also an option with stabilised fillers and can be used in all facial areas but is particularly useful where the skin is very thin, such as in the periorbital area.1 A 30 to 27 gauge cannula injection is appropriate for use in the face and a 25 to 27 gauge cannula for injection in the neck and neckline area.1,3 Punctures or retroinjection points should be 1-1.5cm apart (Figure 2) and these different approaches are shown in Figure 1 and Figure 2.1,19 With a cannula, the dose is still small but the fanning technique is used to distribute the filler from a single entry point (Figure 3).1,19
A regimen of three skin booster treatment sessions four weeks apart in the face, neck and hands has been shown to improve skin elasticity, roughness and skin hydration during a follow-up period of three months.13,17 A study involving 30 people aged 35-65 with a longer follow-up period found that the effects of this regimen lasted for up to 36 weeks in the face and hands.20 Two further studies, involving 131 and 40 participants respectively, with a different regimen and using a different skin boosting HA filler also show improvement in skin texture and hydration lasting up to nine months in the face and hands.21,22
Treatment with skin boosting injectable products is reported to be safe and well-tolerated with adverse effects reported to be mild to moderate and temporary.1,22 Erythema and bruising commonly occur at the injection site and usually resolve within one to two weeks.1 The use of cold or ice packs at the injection site post-treatment can minimise these side effects.1 Pain at the injection site can be mitigated by the use of anaesthesia prior to injection and the application of ice bags to the skin immediately prior to each puncture can be helpful.1 Massaging or moulding the injected area with a cotton stick after injection can help distribute the filler and to minimise any lumps.1,19 Persistent lumps should be treated with hyaluronidase.1 Vascular occlusion is not common in skin boosting treatment due to the small amounts of filler used per puncture, however, aspiration and checking for any reflux of blood are sensible precautions.1
Skin boosting fillers have been shown to restore some elasticity to the skin which may be due to the stimulation of collagen production by the HA itself
HA fillers of any kind, including skin boosters, are contraindicated in pregnant and breastfeeding women due to a paucity of safety data.3,23 Equally, they should not be used in patients undergoing chemotherapy due to the effect on the immune system, nor in patients with active acne due to the link between acne, inflammation and infection.1,3,23 Active infections close to the treatment site can be exacerbated by skin filler or can cause complications by invading the filler site, therefore treatment with fillers should be avoided.1,24
A 2021 updated guideline on safety in facial filler practice recommends that fillers are avoided in many active autoimmune diseases because of potential late-onset immune-mediated reactions.23 This is a complex area with a diversity of professional opinion.25 Patients who are taking anticoagulant medication may be more prone to bruising and should stop taking their medication before treatment with HA fillers if it is acceptable in terms of risk for them to do so.3,26 Use of a cannula to administer the filler can minimise bruising in these patients.1 Patients with body dysmorphic disorder (BDD) can have unrealistic expectations of aesthetic treatment.19 These patients may not benefit from aesthetic treatments and should be referred for further evaluation if BDD is suspected.23,27
HA fillers that can be administered through superficial microinjections have been shown to restore smoothness to skin and to improve elasticity by stimulating de novo collagen production. They offer universal improvement of skin quality and levels of hydration to patients who are seeking a natural appearance but with noticeable reduction in signs of ageing.
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