Forehead Filler

What is forehead filler?

Forehead filler is the placement of hyaluronic acid gel into the tissues of the forehead by injection, to treat hollowing, flatness or contour irregularities. Forehead hollowing is classified as central, on both sides (lateral), mixed, or involving the whole forehead. Depending on the type, the gel is placed either in the layer beneath the muscle or in the layer just under the skin.

According to expert opinion, placing the gel beneath the muscle gives the forehead structural support and also reduces the risks of uneven distribution and vascular complications associated with superficial placement. However, this opinion is at the lowest level of the hierarchy of evidence: it is based on expert experience and descriptions of technique, not on controlled studies. In other words, much of what is said about forehead filler comes from practitioners' experience.

The forehead was once an area treated only with surgery or botulinum toxin. A retrospective study of hyaluronic acid forehead contouring, meaning one that reviewed past patient records, discusses whether deep injections could be a reversible alternative to surgical forehead contouring. The same study also notes that there is no filler designed specifically for the forehead.

When the clinic assesses a product, approval by the US Food and Drug Administration (FDA) is not on its own the deciding criterion; the assessment is based on the product's CE marking, its registration and conformity status in Türkiye, and the manufacturer's intended purpose. You can read what hyaluronic acid is, and how the cross-linked gel used in fillers differs from the one in creams, in the guide article What is hyaluronic acid?.

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Hollowing and flatness of the forehead

The shape of the forehead is not only a matter of age; bone structure and soft tissue vary from person to person. For example, according to an anatomy-based review, the forehead is often narrower in patients of East Asian origin, and the injection technique is adapted to these features. So a flat forehead is not always a sign of loss; it can also be a feature of a person's own structure.

Age-related change happens in more than one layer. In a study that examined the forehead bone with three-dimensional computed tomography, measurable age-related changes were found in the slope of the bone: in both sexes, the length of the lower slope increased with age, and in men over sixty the angle of the upper slope was significantly greater than in younger men. According to the researchers, these findings also help in understanding age-related changes in the soft tissue.

Changes in fat do not go in one direction either. In a study of 100 white women in which the fat compartments of the upper face were followed with magnetic resonance imaging (MRI), the central forehead fat compartment had gained marked volume in the middle-aged group compared with the younger group, and had lost volume in the over-sixty group compared with the middle-aged group. The researchers interpret this as subcutaneous fat (the fat layer under the skin) fluctuating with age. However, the study comes from a single group and cannot be generalised to everyone.

Forehead tissue is thin. In an ultrasound study of 85 people, the total thickness of the soft tissue of the forehead averaged 4.18 mm, and this thickness varied with body mass index and sex. For treatment to be safe and to work, the layers of the forehead need to be understood in detail. Which layer your own hollowing comes from is determined at a consultation.

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Between the brows (glabella): a separate area

The area between the eyebrows (glabella) may look like a continuation of the forehead, but for filler purposes it is treated as a separate, higher-risk area. Hollowing and lines here develop through ageing, muscle movement and tissue loss. The muscles that pull the brows into a frown lie in the same area as the superficial branches of the supratrochlear and supraorbital arteries, which supply the forehead.

Blood vessels in this area lie close to the surface. A study that examined 29 people with ultrasound found small arteries in most people, running at the level of the inner end of the eyebrow, on the midline and just beside it: in 26 of the 29 people, at least one artery was found in the subcutaneous layer (just under the skin) between the brows. These superficial vessels can be connected to the artery of the eye, and this creates a risk of vision loss and stroke.

Another study, which measured the depth of the supratrochlear artery with Doppler ultrasound in 71 cases, found that the depth of the vessel varies from person to person, and with body mass index and age. According to this study, injections between the brows appear risky both under the skin and directly on the bone.

In a retrospective review of 719 filler procedures between the brows, from a single doctor's series, no serious complications were reported. Even so, the same publication stresses that filler between the brows is a high-risk treatment that carries a possibility of skin necrosis and blindness, and that most practitioners should avoid this area. Filler between the brows is often considered together with botulinum toxin, which targets muscle movement.

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Forehead lines: filler or botulinum toxin?

A large proportion of horizontal lines on the forehead and vertical lines between the brows are caused by muscle movement. These lines are mostly treated with medicines from the botulinum toxin group; in other words, the main treatment is botulinum toxin, not filler. Botulinum toxin is often called Botox®, an everyday name that comes from the brand name of a product containing this substance.

In terms of scientific data, the forehead has been studied less than the area between the brows. Of the 65 randomised trials (trials in which participants are randomly assigned to groups) included in a comprehensive review of facial wrinkles, 43 concerned the area between the brows and only two concerned the forehead. In the main comparisons, based on the area between the brows, botulinum toxin type A probably achieved higher success than placebo (a dummy treatment) at four weeks; serious side effects, including drooping eyelid (ptosis), were probably also more frequent.

Filler's place in this picture is static lines that are visible even at rest, and lack of volume. In a randomised split-face study (one side of the face compared with the other) of twenty people, one side received botulinum toxin alone and the other received hyaluronic acid first, followed by botulinum toxin. The two treatments showed similar effectiveness; the combined treatment was associated with a longer-lasting effect on forehead lines that appear with movement and with a greater reduction between the brows at twenty-four weeks. However, the study is small.

According to an anatomy-based expert review as well, using filler and botulinum toxin together can address both lines that form with movement and lines visible at rest. Which type of lines you have is determined at a consultation; botulinum toxin treatment is described in detail on the Botulinum Toxin page.

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How strong is the evidence on forehead filler?

The scientific data on forehead filler consist largely of anatomical studies, reviews describing the technique and small case series. Among the publications reviewed, there is no randomised controlled trial that treated the forehead contour with hyaluronic acid alone and compared it with an untreated group or with another method. The findings on the results of forehead filler should therefore be judged with this limitation in mind.

A retrospective study of the long-term results of hyaluronic acid forehead contouring included 38 patients, 36 of whom were men. The injections were placed just above the periosteum (the membrane covering the bone); during follow-up of up to 36 months, no major or minor complications were reported, and the results were stated to have been maintained. Even so, the researchers stress that randomised controlled trials are needed to determine the ideal gel properties.

In a small series of ten Asian women, a five-step technique was used with highly elastic hyaluronic acid. The aesthetic improvement score was reported as 3.0 immediately after treatment, 2.5 at six months and 1.8 at twelve months; in other words, the effect decreased over time. Mild tenderness and temporary swelling occurred, and no vascular complications were reported. The researchers also note that uneven results were common because of the connective tissue compartments in the forehead, and that the technique took longer to learn than expected.

These two series do not directly complement each other; they used different products, different patient groups and different measures. In addition, a rare complication can be expected not to appear at all in a small series, and this does not show that there is no risk. To understand the nature of the risk, it is therefore necessary to look at reviews that bring together large numbers of cases.

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Limits of this treatment

Forehead filler is intended for volume and contour problems in the forehead; its effect on other concerns is limited. It does not, on its own, remove forehead lines or lines between the brows caused by muscle movement. For these lines, the main treatment is botulinum toxin; filler can play an additional role only in static lines that are visible even at rest.

Ageing of the forehead is not just volume loss, either. Measurable age-related changes have been reported in the slope of the forehead bone, and the central forehead fat compartment has been shown to gain volume in middle age and lose volume in later life. Adding volume does not answer all of these changes in the same way; more volume does not mean a more harmonious forehead.

Hyaluronic acid filler is not permanent; how long the effect lasts varies from person to person and from product to product. It has been reported that there is no filler designed specifically for the forehead and that the ideal gel properties have not yet been established by randomised trials. Permanent fillers, on the other hand, are not a solution but a separate risk: according to a review of complications that led to permanent harm, the permanence of the filler is one of the main factors that determine permanent harm.

The most important limit is the area itself. In the latest update of the reviews collecting cases of filler-related vision loss, the forehead and the area between the brows, together with the nose, were reported as the highest-risk areas. This information matters not to discourage you, but because you need to know it before you decide. Which path makes sense for you (filler, another method or none) is decided by the assessment at your consultation and by your own decision.

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Blood vessels of the forehead

The forehead is supplied mainly by the supratrochlear and supraorbital arteries. According to a study on cadavers (bodies of deceased people examined in medical research), both of these vessels are branches of the artery that supplies the eye (the ophthalmic artery). The same study described more than one pattern of distribution of these vessels in the forehead and found that in some people the deep branch of the supratrochlear artery was absent altogether. The key feature that sets the forehead apart from other areas when it comes to filler is this connection between its blood vessels and the circulation of the eye.

The vessels do not stay in the same layer across the forehead. An ultrasound study of 50 people reported that the deep branch of both arteries passes from beneath the forehead muscle to above it, on average 13 to 14 mm above the rim of the eye socket (orbit); this distance varied widely from person to person. The researchers suggest that the layer directly on the bone can be targeted, but that the superficial layer should be avoided in the lower forehead, because the vessels running on and near the midline are unpredictable.

In another cadaver study, the vessels of 66 heads were examined with computed tomography; in 48 heads, 292 of the 319 arteries crossing the midline of the forehead were reported to run in the superficial layer. According to publications on the supratrochlear artery, the course and branching of this vessel vary considerably from person to person, and the vessel connects with other vessels around the eye. Accidentally entering this network during filler treatment has been linked to vision loss.

The amount needed for a severe outcome is also small. In cadavers, the volume of the section of the supratrochlear artery from between the brows to the top of the eye socket was measured at an average of 0.085 mL. Filler can travel against the direction of blood flow and reach the vessels that supply the eye, and even this small a volume can lead to a severe outcome.

No single method is enough to reduce this risk. A review of vascular occlusion (a blocked blood vessel) lists precautions that include the practitioner's knowledge and skill, the use of a cannula (a fine, flexible tube with a blunt tip), and working with small volumes and low pressure. The review also notes that a check made by pulling back on the syringe (aspiration) cannot reliably confirm that the needle is outside a blood vessel. At this clinic, the doctor chooses a needle or a cannula individually, according to the treatment area and the anatomy.

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Why are the forehead and the area between the brows among the high-risk areas?

The most serious complication of filler treatment is filler entering an artery and disrupting the blood supply to the tissue. As a result, skin necrosis (tissue death) can develop; if the vessels that supply the eye are affected, vision loss can occur. A review of danger zones for blood vessels in the face covers the area between the brows and the nose as separate topics. An analysis that combined studies of vascular occlusion after filler (a systematic review and meta-analysis) also reported the area between the brows, the nose and the nasolabial folds (the lines running from the sides of the nose to the corners of the mouth), which have a complex network of blood vessels, as among the most frequently affected areas.

Reviews collecting reported cases of vision loss worldwide put this picture into numbers. Among the 98 cases in the 2015 review, the highest-risk areas were the area between the brows (38.8%), the nasal region, the nasolabial fold and the forehead (12.2%). In the update collecting 48 new cases published between 2015 and 2018, the nasal region came first (56.3%), followed by the area between the brows at 27.1% and the forehead at 18.8%. In the latest update, which collected 365 new cases between 2018 and 2023, the highest-risk areas were the nose (40.6%), the forehead (27.7%) and the area between the brows (19.0%).

In the latest update, the findings that most often accompanied vision loss were drooping eyelid (ptosis), restricted eye movement, pain and skin changes; stroke-like signs were seen in 19.2% of cases. Of the 318 cases in which the visual outcome was reported, vision did not recover in 68.2% and recovered fully in 6.0%. These rates were compiled from case reports; they show what can happen when the complication occurs, not how often it occurs. This complication is described as rare but devastating, and no treatment has been reported to be consistently successful.

Individual cases reported after forehead injections make the picture concrete. In one case, skin necrosis developed between the brows after hyaluronic acid was injected into the forehead. In another, vision loss developed in one eye hours after a forehead treatment, and areas of impaired blood supply were seen on the forehead and nose; with treatment, vision recovered only to the point of being able to make out hand movements. These are single cases and give no information about how often this happens.

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Known risks

Most filler complications are mild; permanent harm is rare but severe. A meta-analysis combining randomised trials of hyaluronic acid treatments in the face reported the following side effects: swelling, pain, redness, bruising, lumps and firmness you can feel, tenderness, itching and discolouration. This analysis compared side effects by facial area, but the forehead was not included as a separate area. These data are therefore not specific to the forehead and do not come from this clinic.

Filler migration is a separate risk. In one case, swellings developed around the eyes after hyaluronic acid was injected into the forehead; this was assessed as filler migration and a hypersensitivity reaction, and prompt treatment with hyaluronidase gave a good result. This case is also a reminder that, during a filler injection, the practitioner cannot see exactly where the material settles.

A review of complications that led to permanent harm lists the most serious outcomes as vision loss, stroke, chronic granulomatous inflammation (a long-lasting inflammatory reaction to foreign material) and irreversible tissue necrosis. According to this review, the main factors that determine permanent harm are not the amount injected on its own, but the treatment area, incorrect technique and the permanence of the filler. The basis of reducing the risk is knowing the high-risk anatomical areas.

With vascular occlusion, recognising the signs quickly and acting immediately are considered critical to reduce the risk of skin necrosis, scarring and long-term damage. You should find out from your doctor how to contact the clinic if signs appear; you should have been given this information clearly before your treatment.

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Can filler be reversed?

Hyaluronic acid fillers can be dissolved with an enzyme called hyaluronidase; this is the key feature that sets them apart from permanent fillers. According to a review of hyaluronidase treatments, the enzyme can be used for most complications of hyaluronic acid fillers, while emergencies such as vascular occlusion and vision loss require treatment without delay. However, controlled data in this area are limited.

Vision loss is a more serious situation. In a systematic review of cases of filler-related blindness, the possibility of better outcomes in blindness caused by hyaluronic acid than in blindness caused by other fillers was associated with the use of hyaluronidase. On the other hand, reviews collecting cases of vision loss report that no treatment has been found to be consistently successful. So the fact that a filler can be reversed does not mean that the risk is gone.

According to the review of permanent harm, hyaluronic acid fillers continue to be preferred because they can be reversed, whereas permanent fillers increase the risk of long-term complications. Hyaluronidase is kept at the clinic.

If you have had filler in your forehead elsewhere before, the first question is what that filler is. In this case, you are first asked about the type of filler, when it was injected and where; dissolving is not carried out directly on filler of unknown type or filler that cannot be confirmed as hyaluronic acid. If you have any record of the previous treatment, it will be useful at the consultation.

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