Botox Injection Depths & Planes

Most of the words we use to teach toxin injection are borrowed from surgical anatomy, and some of them do more harm than good. "Deep" and "superficial" sound precise until you realise that, on much of the face, the difference between them is only a few millimetres.

This chapter is a practical depth map. It is not a recipe book. It is a framework for thinking about where the bevel ends, why that matters, and why the same stated depth can mean something different on every face you treat.

The Problem With “Deep” and “Superficial”

Yes — on much of the face, the difference between a “deep” and “superficial” Botox injection may be only 2–4 mm. The terminology is therefore potentially misleading.

A 4 mm needle advancement in the orbicularis oculi may pass straight through the muscle and place toxin in an unintended plane. The same 4 mm in the corrugator may be exactly where you want it. And in the masseter, 4 mm is barely past the dermis.

A Better Teaching Framework

Rather than “deep” and “superficial,” teach four approximate planes. Each has a characteristic depth, a set of clinical examples, and a different risk profile.

These figures describe the approximate deposition depth from the uncompressed skin surface, not a rigid needle-insertion measurement. Skin compression, needle angle, sex, BMI, ageing and individual anatomy can change the required penetration substantially.

Practical Facial Botox Depth Map

The table below should be regarded as working clinical ranges rather than universal prescriptions. Use it as a starting point, then adjust for the patient in front of you.

1. Frontalis: Usually About 2 mm, Not “Deep”

The frontalis is a thin muscle closely associated with the superficial musculoaponeurotic system. In most patients, a deposition approximately 1.5–3 mm beneath the skin is sufficient to enter or lie immediately adjacent to it.

Your teaching figure of approximately 2 mm is therefore reasonable.

The important point is that a “superficial frontalis injection” does not necessarily mean intradermal. It normally means through the dermis, with the tip placed just beneath it or within the superficial frontalis. Going deeper does not necessarily improve efficacy because the muscle itself is superficial. It can increase bruising and makes the physical location of the toxin less controlled. Intramuscular forehead injections appear to produce stronger muscular reduction than purely intradermal treatment, but intradermal or very superficial techniques may provide gentler modulation and potentially less brow descent. PubMed

2. Corrugator: Deep Medially, Increasingly Superficial Laterally

This is the clearest example of why one muscle cannot be assigned one depth. The corrugator originates deeply from the medial superciliary arch. As it travels laterally, it becomes more superficial and interdigitates with the frontalis and orbicularis oculi.

Medial corrugator

Your figure of approximately 5 mm is a good working estimate. A typical approach is to pinch or stabilise the muscle, enter perpendicular or nearly perpendicular, and advance approximately 4–7 mm depending on tissue thickness. Some clinicians contact bone and withdraw very slightly before depositing. “Deep” here means deep relative to other mimetic muscles, not necessarily 1 cm deep.

Corrugator body

At the mid-brow, approximately 3–5 mm may be appropriate because the muscle is no longer quite as deep.

Lateral corrugator tail

The lateral fibres become superficial. Treatment is often around 1.5–3 mm, using a superficial intramuscular or immediately subdermal deposition. A deep lateral glabellar injection is undesirable because the levator palpebrae complex lies deeper within the orbit. Eyelid ptosis has been associated with injection too close to the orbital structures, excessive depth, dose and spread. Upper-face ultrasound studies demonstrate considerable individual variation in both the muscle thickness and its distance from the epidermis. PubMed Central (PMC)

3. Procerus: Mid-Depth Rather Than Automatically “To Bone”

The procerus lies over the nasal bones and upper nasal dorsum. A practical depth is around 3–5 mm, depending on the thickness of the skin and subcutaneous tissue. Although some practitioners touch bone, the target is the muscle, not the periosteum.

• Thin skin: approximately 3 mm may reach the target.
• Thicker glabellar tissue: approximately 4–5 mm may be needed.
• Avoid unnecessarily deep or inferior placement.

4. Orbicularis Oculi: Extremely Superficial

The orbicularis oculi is one of the thinnest facial muscles. A 2025 ultrasound study reported a mean muscle thickness of approximately 1.56 mm and a mean depth from the surface of approximately 1.63 mm, with considerable regional variation and the muscle lying less than 1 mm deep at some measured points. PubMed

That means crow’s-feet injections are normally about 1–2.5 mm deep, subdermal or very superficial intramuscular, often placed with the bevel visible beneath the skin. A 4–5 mm injection in this area is not “a little deeper”; it may pass through the orbicularis and place toxin in an unintended deeper plane.

Lower eyelid

For pretarsal or infraorbital treatment, deposition is commonly intradermal or immediately subdermal, approximately 1–2 mm, with very small doses. This is an advanced treatment because excessive weakening can cause lower-lid laxity, altered smile mechanics, oedema or dry-eye symptoms.

5. Nasalis and Bunny Lines

The transverse nasalis is generally superficial over the lateral nasal wall. Approximate depth is 2–4 mm, in the superficial intramuscular plane. In a thin nose, 2 mm can be sufficient.

The central lesson is not to follow the wrinkle too far laterally and inferiorly because some “bunny lines” are generated by the levator labii superioris alaeque nasi, not only the nasalis.

6. Gummy Smile and Nasal Elevators

The upper-lip elevator muscles are deeper than orbicularis oris but are still relatively small. For the levator labii superioris alaeque nasi or overlapping elevator point, approximate depth is 3–5 mm, occasionally up to around 6 mm in thicker tissue, with targeted intramuscular deposition.

Depth alone does not create accuracy here. A few millimetres of horizontal error may affect the wrong elevator and create smile asymmetry.

7. Lip Flip and Perioral Orbicularis

The orbicularis oris is superficial. Approximate depth is 1–2 mm, in the immediately subdermal or superficial muscle plane. The aim is limited modulation of the peripheral fibres, not a deep injection into the substance of the lip.

Deep placement can produce excessive oral incompetence, altered speech, difficulty drinking or an asymmetric smile.

8. DAO: Approximately 3–5 mm

Recent high-frequency ultrasound research in 290 Caucasian patients found a mean DAO depth from the skin of 3.1 mm, greater depth in overweight or obese patients, lateral displacement from traditional landmarks in nearly 80% of subjects, and occasional overlap with the depressor labii inferioris. PubMed

This supports a practical DAO deposition around 3–5 mm, but the study also shows why a fixed surface point and a fixed depth are imperfect. The objective is to enter the DAO without moving medially into the depressor labii inferioris, which can produce lower-lip asymmetry.

9. Mentalis: Deeper and Close to the Mandible

The mentalis originates from the incisive fossa of the mandible and inserts into the chin skin. A practical technique is generally approximately 4–7 mm deep, deep intramuscular, often toward the mandible, followed by slight withdrawal if bone is contacted.

Very superficial toxin may reduce skin dimpling but incompletely control the deeper mentalis contraction. Conversely, excessive lateral spread may weaken the depressor labii inferioris or orbicularis oris.

10. Masseter: Genuinely Deep Compared With Mimetic Muscles

The masseter is entirely different from the thin muscles of facial expression. Typical deposition depths may be 8–12 mm in a thinner patient, 12–15 mm or more in a thick or hypertrophic masseter. The objective is intramuscular placement, usually within the lower safe portion of the muscle.

The masseter has layered anatomy, internal tendinous structures and variable nerve distribution. Blind injections repeatedly delivered into the same region may also encounter localised fibrosis, which can alter treatment response. PubMed

A standard 13-mm needle may not reliably reach the intended depth in every large masseter, especially when inserted obliquely.

11. Platysma: Superficial Despite Being in the Neck

Platysma lies immediately beneath the subcutaneous tissue. Approximate depth is 2–4 mm, in the superficial intramuscular plane. Grasping a platysmal band can help isolate it.

A very deep neck injection risks affecting deeper strap muscles and swallowing mechanics. The treatment should remain in the visibly or palpably contracted platysma.

The Most Useful HSI Teaching Rule

Rather than teaching “deep” and “superficial” as vague words, teach four approximate planes:

Angle Matters as Much as Depth

Depth alone does not describe an injection. Two practitioners can enter the same skin point, advance the same 5 mm, and deposit toxin in two entirely different muscles. The variable they have changed is not depth but vector — the angle of entry and the direction of travel.

The corrugator is the clearest teaching example. Enter at the medial brow at 90 degrees and travel 5 mm and the bevel typically ends within the corrugator body, close to the superciliary arch. Enter at the identical surface point at 45 degrees angled superiorly and travel the same 5 mm and the bevel may finish 3–4 mm higher in the tissue column — within the frontalis, above the intended target. The dose was correct. The depth reading was correct. The muscle was wrong.

This is why the direction the needle points should be dictated by where the product is intended to sit, not by habit or by the practitioner’s hand position.

Trigonometry is unforgiving here. At 90 degrees, 5 mm of needle equals roughly 5 mm of vertical depth. At 45 degrees, the same 5 mm of needle produces only about 3.5 mm of vertical depth and roughly 3.5 mm of lateral displacement. At 30 degrees it is approximately 2.5 mm vertical and 4.3 mm lateral. The needle has not changed. The destination has.

Add to this the effect of skin compression, pinching, and the fact that toxin does not remain at the tip of the needle — it spreads along the path of least resistance, which frequently follows fascial planes rather than the direction the practitioner intended.

The Critical Qualification

A stated “5-mm injection” does not guarantee that the toxin is 5 mm beneath the natural skin surface because:

• The needle may compress the skin by 1–3 mm.
• An oblique needle travels farther but reaches less perpendicular depth.
• The bevel itself is approximately 1 mm long.
• Muscle thickness and depth vary between points on the same face.
• Pinching can lift the muscle away from deeper structures.
• Age, sex and facial adiposity change the distance to the target.

So for trainees, phrase the concept as: depth is not primarily how much needle disappears. It is the anatomical layer in which the bevel ends.

Frontalis is normally reached at roughly 2 mm. The medial corrugator may require roughly 5 mm. The lateral corrugator then becomes superficial again. Orbicularis oculi may be only 1–2 mm beneath the surface.

The literature supports this layer-based approach, but it does not provide a universally validated millimetre prescription for every facial injection point. Ultrasound studies increasingly demonstrate that variation between patients can be as important as the average measurement. PubMed Central (PMC)