Every time you look in the mirror, do you notice hollowness in your temples and wrinkles on your forehead?
"My face somehow looks older"——in most cases, the culprit isvolume loss.
- Hyaluronic acid injectioninto temples and foreheadMechanism and latest techniques
- Detailed comparison between hyaluronic acid injection and autologous fat transfer (fat grafting) and differences in integration rates
- Major risks lurking in temple and forehead areas, such as blindness and stroke, and strategies to avoid them
Because these are delicate facial features that greatly influence facial impression and youthfulness, it is natural to think, "I don't want to fail" and "I want to 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 surgery," the forehead and temples are particularly prone to anatomical risks among facial areas——a"high-risk area."If you undergo treatment without proper knowledge, you risk causing irreversible serious complications.
This article, based on numerous international clinical studies and the latest anatomical data, provides a thorough explanation of risk-avoidance knowledge and techniques practiced by leading physicians. By the end of your reading, you should have clarity on "where, what, and why you should verify."
First, what you should know——the aging mechanism of the forehead and temples and the science of hyaluronic acid
What does "loss of firmness" mean?
Changes in the mechanical properties of skin (firmness and elasticity) are one of thefirst measurable signsof skin aging, and in most cases, this is followed by the formation of visible wrinkles. Hyaluronic acid (HA)-based fillers, due to their efficacy and safety, have beenfor over 20 yearshas been widely used as the "gold standard" in skin rejuvenation.
In the past, hyaluronic acid was perceived merely 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 neo-collagenesis effect
Here is a fact that many patients are unaware of.
From clinical observations of patients who have repeatedly received hyaluronic acid injections, unexpected findings have been reported, includingsustained long-term effectsbeyond what would be predicted by hyaluronic acid's lifespan and improvements in the mechanical properties of the skin.
Why does this happen?
The mechanism works as follows: The injected cross-linked hyaluronic acid physically stretches the extracellular matrix (ECM) and imparts mechanical tension to fibroblasts. This tension stimulates fibroblasts, promoting the synthesis of new collagen (particularly Type I and Type III collagen) and elastin (neo-collagenesis).
In other words, hyaluronic acid not only adds physical volume but also serves as a "skin booster" that stimulates the generation of youthful skin components and rebuilds the dermal scaffold.
Injection technique is all about "which layer to inject into"
The soft tissue of the human forehead is divided mainly into three layers: first, the "deep layer (behind 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 the frontalis muscle. The forehead skin is the thickest on the face, with septa running 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 at the 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 while simultaneously influencing 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 grafting)" is frequently compared. It may seem "safe if we use our own fat," but the reality is somewhat more complex.
The appeal and reality of autologous fat transfer
Since fat transfer was first reported by Dr. Neuber in 1893, it has become a common technique due to the ease of harvesting, abundant volume, and lack of rejection. Adipose tissue is autologous, completely biocompatible, naturally integrates into host tissue, and is said to possess the characteristics of an ideal filler with potentially "permanent" results.
In the representative technique "Structural Fat Grafting," a blunt needle (cannula) is inserted through a 2mm 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 facial procedures, the maximum amount of fat placed during a single cannula withdrawal is typically1/10 mL.
The biggest challenge of fat grafting——why is engraftment rate "a matter of luck"?
This is the point that surprises many patients after surgery.
The greatest drawback of autologous fat grafting isunpredictable absorption rateand variable retention rates (Chou 2017, Lv 2020). According to Dr. Carpaneda's 1993 theory, transplanted fatty tissue must obtain nutrition through infiltration (osmosis) from surrounding tissue fluid during the initial phase before neovascularization of capillaries occurs.
Therefore, only tissue within a range of1.5±0.5 mmfrom the margin of the transplanted fat can survive, and the survival rate is emphasized to be only approximately40%If large fat parcels exceeding a radius of 2 mm are injected, nutrients do not reach the center, creating a risk of fat necrosis and liquefaction in the center due to sustained ischemia and hypoxia. This is the primary cause of nodule and cyst formation following fat grafting.
So, what does objective data show?
A systematic review and meta-analysis on volume retention rates in facial fat grafting (based on studies selected from2138records) reveals the following facts.
- In volume measurement, there is a difference in measured values between 3D scanning and CT imagingsignificant difference (p = 0.01)and CT may overestimate the retention rate
- Regarding fat processing techniques (centrifugation, filtration, precipitation), there is no clear significant evidence for which is superior, but the centrifugation and filtration groups tend to show better results than the precipitation group
- The second fat injection shows a significantly higher volume retention rate (engraftment rate) compared to the first injectiontend to
MAFT——A technical breakthrough in "micro-injection"
To overcome these challenges, "Micro-autologous Fat Transplantation (MAFT)" was developed.
Using specialized precision equipment (MAFT-GUN), with each trigger pull1/60 to 1/240 mL(primarily 1/120 mL on the forehead, that is, 0.0083 mL) of extremely fine fat particles are injected consistently.
What were the results?178 patients (167 female, 11 male)underwent a clinical study of MAFT, in which during a follow-up period of an average of34 months, complications such as neurovascular injury, skin necrosis, abscess, nodule formation, and calcification were not observed, and83.1% of patients showed favorable results("very satisfied" in 34.8%, "satisfied" in 48.3%), according to reports.
In the end, which should you choose——the crux of the comparison
While fat grafting aims for permanent results, hyaluronic acid is temporary but has clear advantages: results are easier to predict in advance, and downtime is shorter. Hyaluronic acid fillers (especially products with high viscoelasticity and cohesiveness) excel in tissue lifting power and structural support.
On the other hand, there is notable data not to be overlooked. According to reports citing past literature (Lee SK, 2015), in filler injection to the forehead, allergic reactions (25%)、filler material migration (12.5%）、necrosis and thromboembolism due to injection (25%）、foreign body granuloma (37.5%), and other complications have been reported in some cases. Additionally, hyaluronic acid products contain cross-linking agents (such as BDDE), and small fragments of hyaluronic acid carry inherent risks of triggering inflammation and inducing adverse effects such as erythema, mild edema, hematoma, itching, and pain.
However, a decisive difference emerges here—modern hyaluronic acid fillers have an antagonist agent called "hyaluronidase" (dissolving injection) (DeVictor 2021). We will explain in detail in the next section why this is important.
Unknown dangers—the reality of "blindness and stroke" risks hidden in temple and forehead injections
From here on is the most important part of this article.
In aesthetic medicine, injection into the temples or forehead is considered a "high-risk procedure." The primary reason is theextremely complex vascular network running through the upper faceis located.
Facial blood vessels have "two systems" that connect
The face receives blood supply from both the internal carotid artery (ICA) system and the external carotid artery (ECA) system, and these blood vessels form complex anastomoses (vessel connections) in 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 temple region.
If filler or fat is accidentally injected into an artery, the substance may flow backward through the artery due to injection pressure and reach the internal carotid artery system. Once the 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 frightening reality revealed by 61 cases of clinical data
This is not theoretical. Look at the actual data.
In a systematic review of arterial embolism (AE) occurring after facial fat injection, the average age was33.56±11.45 yearsof61 patientswith detailed data analysis. Although this data is from fat injection, the occurrence mechanism is identical in hyaluronic acid injection, making it an important indicator of the danger of injection sites.
- Most dangerous injection sites:The injection sites most frequently associated with arterial embolism were "glabella only, or multiple facial regions (full face, etc.)" (each 26.2%, 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 volume injected: The average injection volume when embolism occurred was 21.5±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 dysfunction (loss of consciousness or hemiplegia, etc.) (34.5%, n=20/58), and cases where both visual impairment and neurological dysfunction developed accounted for 22.4% (n=13/58)
- Location of occluded artery:Occlusion of the ophthalmic artery (OA) occurred in 43.3% (n=26/60), occlusion of the anterior cerebral artery or middle cerebral artery (CA) in 18.3% (n=11/60), and occlusion of both in 23.3% (n=14/60)
- Final prognosis:Many of these complications result in extremely serious outcomes, including permanent blindness, severe neurological dysfunction (stroke), or death
Understanding mild to moderate side effects as well
While overshadowed by major risks, it is important to be aware of more common side effects. Common side effects of hyaluronic acid injection include transient erythema, edema (swelling), bruising, and pain or discomfort at the injection site. Although this is data from non-surgical rhinoplasty (NSR), complications associated with hyaluronic acid fillers include bruising (1.58%), hematoma (0.13%）などが報告されています（DeVictor 2021）。また、ヒアルロン酸の注射後に一時的なアレルギー反応や、遅発性の肉芽腫や結節形成が起こるリスクもゼロではありません（Kim 2020、DeVictor 2021）。
So how can we ensure safety? — 4 Key Safety Measures to Minimize Risk
Now that we understand the risks, the next important question is: "How do we avoid those risks?"
There are no standardized treatment guidelines for arterial embolism following upper-face injection. While hyaluronic acid has hyaluronidase as a dissolving agent,no equivalent antidote exists for fat embolism, which is why prevention becomes absolutely fundamental, especially in fat transfer procedures.
1. Use of blunt cannulas and size selection
Needle diameter and shape directly correlate with the risk of perforating blood vessel walls. Blunt-tipped cannulas require significantly greater force to penetrate vessel walls compared to sharp needles, providing a theoretical basis for reducing the risk of intravascular injection. Furthermore, larger-diameter cannulas (such as 18 gauge) are considered safer than thinner needles. However, arterial embolism has been reported even with cannula use, so they are not completely risk-free.
2. Control all three factors: injection speed, pressure, and volume
To prevent retrograde flow into blood vessels during injection, it is essential to inject at an extremely slow speed and with low pressure. For each injection pass, 0.1 cc or less of small aliquots (aliquoting technique) is recommended. While aspiration testing — drawing back on the syringe before injection to confirm no blood return — is recommended, animal studies have shown its reliability is not absolute (blood may not return even if the needle is in a vessel), so aspiration testing alone should not be relied upon (per safety guidance on HA injection by Trevidic 2022).
3. Precise approach to anatomically correct tissue planes
It is extremely important to avoid layers where blood vessels are densely concentrated. In the forehead and temples, injection typically occurs in deeper, safer planes such as the periosteum with relatively fewer blood vessels, to rebuild structural volume. The practitioner must have complete understanding of the three-dimensional vascular course and tissue planes of the face.
4. Immediate hyaluronidase response protocol — the greatest strength of hyaluronic acid
This is precisely where the greatest advantage of choosing hyaluronic acid lies. If vascular occlusion is suspected (signs such as skin blanching, severe pain, or visual disturbances), 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 permanent sequelae were prevented by administering hyaluronidase early after signs of ischemia appeared (DeVictor 2021).
The ability to "dissolve" the filler — perhaps this is the most fundamental difference between hyaluronic acid and fat transfer.
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 the self-generation of collagen, functioning as a "skin booster"
- Difference from fat transfer (fat grafting):Autologous fat transfer offers semi-permanent results but has unpredictable absorption rates and risks of firm nodules from central necrosis. The latest MAFT technology injects ultra-small parcels of 1/120 mL to improve engraftment rate and safety. By contrast, hyaluronic acid provides temporary results, but with the major advantage of easy-to-predict outcomes and the existence of hyaluronidase as a dissolving enzyme in case of complications
- Forehead and temples are high-risk areas:Due to the complex vascular network in this region, mistaken intraarterial injection can cause retrograde flow into the ophthalmic or cerebral arteries, triggering 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 embolism
- Absolute requirements for safe treatment:Thorough knowledge of anatomy, proper use of blunt cannulas, slow injection at low pressure in small volumes, and rapid hyaluronidase response in case of complications are the absolute keys to preventing irreversible accidents
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References
- Ma Y, Jin M, Zhen Y, et al. Advances of Hyaluronic Acid Nasal Injection Techniques and Complications: A Systematic Review. Aesthetic Plastic Surgery. 2025DOI
- Ma Y, Jin M, Zhen Y, et al. Advances of Hyaluronic Acid Nasal Injection Techniques and Complications: A Systematic Review. Aesthetic Plastic Surgery. 2025DOI
- 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
- 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
- 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
About the author of this article
Hiromitsu NakamuraPhysician, Ginza Clinic
Zetith Beauty Clinic Ginza, Shinsaibashi Osaka, and Fukuoka branches
With a track record of presenting research 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 principles and pursues natural-looking results tailored to each individual's skeletal structure and tissues.