Hyaluronic acid injection in temples and forehead: Technique, comparison with fat transfer, and risks

Every time you look in the mirror, are you bothered by hollowness in your temples and wrinkles on your forehead?

"Somehow my face looks older"——the cause is oftenvolume lossin the temples and forehead.

• Mechanism and latest techniques forhyaluronic acid injectionin temples and forehead
• Detailed comparison of hyaluronic acid injection and autologous fat transfer (fat grafting), and differences in retention rates
• Major risks lurking in temple and forehead areas such as blindness and stroke, and strategies to avoid them

Because this is a delicate area that greatly influences facial impression and youthfulness, it is natural to want to "avoid failure" and "choose the safest and most effective method."

However, there is an important fact you should know.

Although hyaluronic acid injection is often called "minor cosmetic procedure," the forehead and temples are particularly anatomically dangerous areas of the face——a"high-risk area."Without proper knowledge, treatment can lead to serious and irreversible complications.

This article thoroughly explains the knowledge and techniques for risk avoidance practiced by leading physicians, based on numerous international clinical studies and the latest anatomical data. By the time you finish reading, you should have a clear understanding of "where, what, and why you should verify."

First, what you need to know——aging mechanisms of the forehead and temples, and the science of hyaluronic acid

"Loss of firmness"——what does this mean?

Changes in the mechanical properties of skin (firmness and elasticity) are one of thefirst measurable signsof skin aging, and in many cases, visible wrinkles form subsequently. Hyaluronic acid (HA)-based fillers, due to their efficacy and safety,for over 20 yearshas been widely used as the "gold standard" in skin rejuvenation.

In the past, hyaluronic acid was perceived simply as a "filler" for wrinkles and grooves. However, as understanding of the facial aging process has deepened, it has come to be utilized as "3D volumization" to compensate for age-related facial volume loss.

Beyond mere "filling"—the Neocollagenesis effect

Here lies a fact that many patients are unaware of.

From clinical observations of patients who have undergone repeated hyaluronic acid injections, findings beyond what would be expected from hyaluronic acid's known lifespan have been reported:Sustained long-term effectsand improvements in skin mechanical properties.

Why does this happen?

The mechanism works as follows: Injected cross-linked hyaluronic acid physically stretches the extracellular matrix (ECM), applying mechanical tension to fibroblasts. This tension stimulates fibroblasts, promoting the new synthesis (neocollagenesis) of collagen (particularly Type I and Type III collagen) and elastin.

In other words, hyaluronic acid not only adds physical volume but also acts as a "skin booster" that stimulates the generation of youthful skin components and reconstructs the dermal scaffold.

Injection technique is all about "which layer to inject into"

The soft tissue of the human forehead is primarily divided into three layers. First, the "deep layer (posterior to the frontalis muscle)" on the periosteum of the frontal bone; second, the "middle layer (within the frontalis muscle)" with abundant blood flow; and third, the "superficial layer (subcutaneous tissue)" between the dermis and frontalis muscle. The forehead skin is the thickest on the face, and septa run laterally from the dermis toward the frontalis muscle.

For deep horizontal forehead wrinkles, a technique using reconstituted (diluted) hyaluronic acid (for example, diluted to a concentration of 16 mg/mL with 1% lidocaine and epinephrine) injected directly into the depth of the wrinkles (approximately mid-dermal level) using a serial threading technique has been reported. On the other hand, for extensive volume loss in the temples and forehead, an approach to deeper layers (such as above the periosteum) is important to provide structural support.

"Where and at what depth to inject" — this is what determines results, and at the same time, influences the risks discussed later.

Hyaluronic acid vs. autologous fat transfer — which is right for you?

In forehead and temple volume restoration, alongside hyaluronic acid injection, "autologous fat transfer (fat graft)" is frequently compared. It may seem "safe if using your own fat," but the reality is somewhat more complex.

The appeal and reality of autologous fat transfer

Since fat transplantation was first reported by Dr. Neuber in 1893, it has become a common technique due to the ease of harvesting, abundant volume, and absence of rejection reactions. Adipose tissue is autologous, completely biocompatible, naturally integrates with host tissue, and is said to possess the characteristics of an ideal filler potentially delivering "permanent" results.

In the representative technique "Structural Fat Grafting," a blunt needle (cannula) is inserted through a 2 mm incision, and fat is injected only as the cannula is withdrawn, placing it in a natural tissue plane so that host tissue collapses around the fat. In the face, the maximum amount of fat typically placed in a single cannula withdrawal is1/10 mL.

The greatest challenge of fat transfer — why is the "take" rate "a matter of luck"?

This is the point that surprises many patients after surgery.

The biggest drawback of autologous fat injection isunpredictable resorption rateand variability in graft take-rate (Chou 2017, Lv 2020). According to Dr. Carpaneda's 1993 theory, transplanted adipose tissue must obtain nutrition through osmosis from surrounding tissue fluid during the initial phase until neovascularization of capillaries occurs.

For this reason, only tissue within1.5±0.5 mmfrom the margin of the transplanted fat can survive, and the survival rate is emphasized to be approximately40%If large fat globules (parcels) exceeding a radius of 2 mm are injected, the central portion does not receive sufficient nutrition, and there is a risk that the central fat will undergo necrosis and liquefaction due to sustained ischemia and hypoxic conditions. This is the primary cause of nodule (nodular) and cyst formation after fat injection.

So, what does objective data show?

A systematic review and meta-analysis regarding volume retention rate of facial fat transplantation (based on studies carefully selected from2,138records) reveals the following facts:

• In volumetric measurement, there isa statistically significant difference (p = 0.01)between measurements by 3D scan and CT, and CT may overestimate take-rate
• Regarding fat processing techniques (centrifugation, filtration, sedimentation), there is no clear significant evidence for which is superior, but the centrifugation and filtration groups tend to show better results than the sedimentation group
• Second fat injection showsa tendency to have much higher volume retention rate (take-rate) than the first injection

MAFT—A technical breakthrough: "Micro-injection"

To overcome these challenges, "Micro-autologous Fat Transplantation (MAFT)" was developed.

Using dedicated precision equipment (MAFT-GUN), with each trigger pull,1/60–1/240 mL(primarily 1/120 mL, or 0.0083 mL on the forehead) of extremely fine fat particles are injected consistently.

What were the results?178 patients (167 female, 11 male)were the subject of a clinical study on MAFT. In a follow-up survey over an average of34 months, no complications such as neurovascular injury, skin necrosis, abscess, nodule formation, or calcification were observed, and83.1% of patients showed favorable results("very satisfied" 34.8%, "satisfied" 48.3%), according to reports.

So which should you choose—the core of the comparison

While fat injection aims for permanent results, hyaluronic acid is temporary but offers clear advantages: results are easier to predict beforehand and downtime is shorter. Hyaluronic acid fillers (especially products with high viscoelasticity and cohesivity) excel in tissue lifting and structural support.

However, there is overlooked data. According to a report citing past literature (Lee SK, 2015), in filler injection to the forehead, complication rates were reported including allergic reactions (25%), filler material migration (12.5%), necrosis and embolism from injection (25%), foreign body granuloma (37.5%), and more. Additionally, hyaluronic acid products contain cross-linking agents (such as BDDE), and small fragments of hyaluronic acid carry inherent risks of triggering inflammation and adverse effects such as erythema, mild edema, hematoma, itching, and pain.

However, a decisive difference emerges here—modern hyaluronic acid fillers have an antagonist called "hyaluronidase" (dissolution injection) (DeVictor 2021). Why this matters will be explained in detail in the next section.

Scary if you don't know—the reality of "blindness and stroke" risks lurking in temple and forehead injection

This is the most important part of this article.

In aesthetic medicine, injection to the temples or forehead is considered a "high-risk procedure." The biggest reason is theextremely complex vascular network running through the upper faceis located in.

The blood vessels on the upper face are "connected in two systems"

The face receives blood supply from both the internal carotid artery (ICA) system and external carotid artery (ECA) system, and these blood vessels form complex interconnections (vascular anastomoses) on the upper face. For example, the trochlear artery and supraorbital artery, which are terminal branches of the ophthalmic artery, exist in the glabellar region, and blood vessels such as the superficial temporal artery run through the temporal region.

If filler or fat is accidentally injected into an artery, the substance may flow retrograde within the artery due to injection pressure and reach the internal carotid artery system. Once injection pressure is released, embolic material (hyaluronic acid or fat) is carried by blood flow and can occlude critical blood vessels such as the ophthalmic artery or cerebral artery.

The alarming reality revealed by clinical data from 61 patients

This is not theory. Look at the actual data.

In a systematic review of arterial embolism (AE) occurring after facial fat injection, the data of61 patientswith an average age of33.56±11.45 years oldwere analyzed in detail. Although this data concerns fat injection, the mechanism of occurrence is identical in hyaluronic acid injection, making it an important indicator of the danger of injection sites.

• Most dangerous injection sites:The most common injection sites that caused arterial embolism were "glabella only, or multiple facial regions (full face, etc.)" (each26.2%, n=16/61). Followed by "temples" (16.4%, n=10/61), and "forehead" (14.8%, n=9/61)——the numbers clearly demonstrate how high-risk the forehead and temple areas are
• Average injected volume:The average injection volume when embolism occurred was21.5±21.5 mL.
• Symptoms that developed:Visual impairment (decreased vision or blindness) was the most frequently reported (41.4%, n=24/58), followed by neurological disorders (such as loss of consciousness or hemiplegia) (34.5%, n=20/58), and cases in which both visual impairment and neurological disorders occurred also reached22.4%(n=13/58)
• Location of occluded artery:Occlusion of the ophthalmic artery (OA) occurred in43.3%(n=26/60), occlusion of the anterior cerebral artery or middle cerebral artery (CA) in18.3%(n=11/60), and occlusion of both in23.3%(n=14/60)
• Final prognosis:Many of these complications result in extremely serious outcomes, including permanent blindness, severe neurological disorders (stroke), or death

Understanding mild-to-moderate side effects

While overshadowed by major risks, it is important to be aware of more common side effects as well. Common side effects of hyaluronic acid injection include transient erythema, edema (swelling), bruising, and pain or discomfort at the injection site. Although data from non-surgical rhinoplasty (NSR), complications from hyaluronic acid fillers include bruising (1.58%), hematoma (0.13%）and other cases have been reported (DeVictor 2021). Additionally, there is a non-zero risk of temporary allergic reactions, delayed granulomas, and nodule formation after hyaluronic acid injection (Kim 2020, DeVictor 2021).

So how do we stay safe — 4 essential safety measures to minimize risk

Now that we understand the risks, the next important question is: "How do we avoid these risks?"

There are no standardized treatment guidelines for arterial occlusion from injection in the upper face. While hyaluronic acid has hyaluronidase as a dissolving agent,there is no equivalent antagonist for fat embolismtherefore, prevention is an absolute foundation, especially in fat grafting.

1. Use of blunt needles (blunt cannulas) and appropriate sizing

Needle thickness and shape directly correlate with the risk of vascular wall perforation. Blunt cannulas with rounded tips require greater force to penetrate blood vessel walls compared to sharp needles (hypodermic needles), providing a theoretical basis for reducing the risk of intravascular injection. Furthermore, larger (thicker) cannulas (for example,18 gaugeand others) are considered safer than thinner needles. However, even when using cannulas, reports of arterial occlusion exist, so it is not completely risk-free.

2. Control of injection speed, pressure, and volume — all three must be managed

To prevent retrograde flow into blood vessels during injection, it is essential to inject at an extremely slow speed using low pressure. For each injection pass,0.1 cc or lessof small-volume sequential injections (aliquots) are recommended. Additionally, while the "aspiration test"—drawing back on the syringe before injection to confirm no blood reflux—is recommended, its reliability is not complete in animal studies and similar settings (blood may not be withdrawn despite the needle being inside a vessel), and aspiration testing alone should not be relied upon (per Trevidic 2022 safety recommendations for HA injection).

3. Precise approach to anatomically correct layers

It is extremely important to avoid areas with dense vasculature. In the forehead and temples, the approach typically involves deep injection into relatively safe planes with fewer vessels, such as above the periosteum (deeper layer), to rebuild structural volume. The surgeon must have complete understanding of the three-dimensional vascular anatomy and layer structure of the face.

4. Immediate hyaluronidase response protocol — this is hyaluronic acid's greatest strength

This is precisely where the greatest advantage of choosing hyaluronic acid lies. If vascular occlusion is suspected (skin blanching, severe pain, visual abnormalities, etc.), immediate local injection of hyaluronidase can break down the hyaluronic acid and halt the progression of tissue necrosis or vision loss. Multiple studies have reported cases where early hyaluronidase administration after signs of ischemia appearedprevented permanent complications(DeVictor 2021).

"The option to dissolve it" — this may be the most fundamental difference between hyaluronic acid and fat grafting.

Summary of this article

• Rejuvenation and neocollagenesis:Hyaluronic acid is not merely a volume filler; by stretching the extracellular matrix, it stimulates fibroblasts and promotes self-generation of collagen—functioning as a 'skin booster'
• Difference from fat grafting:Autologous fat grafting can provide semi-permanent results, but the resorption rate is unpredictable, and there is a risk of nodule formation from central necrosis. The latest MAFT technique injects ultra-small parcels of 1/120 mL to improve graft take and safety. In contrast, while hyaluronic acid results are temporary, they are easily predictable, and the existence of a dissolving enzyme (hyaluronidase) in case of emergency is a major advantage
• Forehead and temples are high-risk areas:Due to the complex vascular network in this region, accidental intra-arterial injection can cause retrograde flow to the ophthalmic or cerebral arteries, creating a risk of extremely serious complications such as blindness or stroke. Clinical data shows that the temples (16.4%) and forehead (14.8%) are major sites of arterial occlusion events
• Essential conditions for safe treatment:Thorough knowledge of anatomy, proper use of blunt cannulas, slow injection with low pressure and small volumes, and rapid hyaluronidase response in case of complications are the absolute keys to preventing irreversible accidents

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References

1. Ma Y, Jin M, Zhen Y, et al. Advances of Hyaluronic Acid Nasal Injection Techniques and Complications: A Systematic Review. Aesthetic Plastic Surgery. 2025DOI
2. Ma Y, Jin M, Zhen Y, et al. Advances of Hyaluronic Acid Nasal Injection Techniques and Complications: A Systematic Review. Aesthetic Plastic Surgery. 2025DOI
3. Liew S, Scamp T, de Maio M, et al. Efficacy and Safety of a Hyaluronic Acid Filler to Correct Aesthetically Detracting or Deficient Features of the Asian Nose: A Prospective, Open-Label, Long-Term Study. Aesthetic Surgery Journal. 2016DOI
4. Rho N, Youn C, Youn S, et al. A comparison of the safety, efficacy, and longevity of two different hyaluronic acid fillers in filler rhinoplasty: A multicenter study. Dermatologic Therapy. 2021DOI
5. Trevidic P, Kim H, Harb A, et al. Consensus Recommendations on the Use of Hyaluronic Acid–Based Fillers for Nonsurgical Nasal Augmentation in Asian Patients. Plastic & Reconstructive Surgery. 2022DOI

Author of this article

Hiromitsu NakamuraPhysician, Ginza Clinic

Zetith Beauty Clinic Ginza, Shinsaibashi Osaka, and Fukuoka Clinics

With a track record of research presentations at domestic and international academic conferences, he is involved in technical guidance and education across all Zetith Beauty Clinic locations. He specializes in precision aesthetic medicine based on anatomical evidence, pursuing natural results tailored to each individual's bone structure and tissue composition.