What are the four main types of injections ?
The four main injection routes used in medicine are intradermal injection, subcutaneous injection, intramuscular injection, and intravenous injection.
This classification is based on the tissue into which the needle delivers the product.
The choice of administration route depends on the medicine or product used, the desired speed of action, its absorption process and the medical indication.
What is an intradermal injection ?
An intradermal injection involves administering a small quantity of product into the dermis, the layer of skin beneath the epidermis.
This route is used particularly for certain diagnostic tests, such as the tuberculin skin test, and for some vaccinations.
The quantity injected is generally small because the dermis has a limited capacity to receive a large volume.
In aesthetic medicine, certain techniques also use very superficial injections. This is particularly the case with some mesotherapy techniques.
However, the exact depth remains determined by the product, the technique used and the intended objective.
What is a subcutaneous injection ?
A subcutaneous injection delivers the product into the hypodermis, meaning the tissue beneath the skin, which includes fatty tissue.
This route generally allows more gradual absorption than intravenous administration.
It is commonly used for certain medicines such as insulin or low-molecular-weight heparins.
The thickness of subcutaneous tissue varies considerably between body regions and individuals. The choice of injection site, needle and technique must therefore suit the treatment administered.
In aesthetic medicine, the subcutaneous plane may also be used for certain treatments, particularly when a product needs to act on volume or tissues beneath the dermis.
What is an intramuscular injection ?
An intramuscular injection, or IM, involves administering a medicine directly into a muscle.
Muscles have a richer blood supply than subcutaneous tissue. This blood supply enables the absorption of many medicines administered by this route.
Intramuscular injections are used particularly for certain vaccines and medicines.
The most frequently used sites depend on the patient’s age, the volume to be administered and the product concerned. The deltoid muscle in the arm is, for example, a common vaccination site in adults.
The intramuscular route should not be confused with an injection into a muscle for local therapeutic purposes. Botulinum toxin, for example, can be injected into precisely selected muscles to temporarily reduce their activity. The aim is then not to achieve systemic absorption of the product, but a targeted local action.
What is an intravenous injection ?
An intravenous injection, or IV, allows a product to be administered directly into the bloodstream through a vein.
Unlike intradermal, subcutaneous or intramuscular injections, there is no absorption phase through the tissues before the product reaches the circulation.
This route therefore makes the administered product immediately available.
It is used in many situations : administering medicines, infusions, hydration, contrast agents or treatments requiring precise control of the dose and administration rate.
This speed also calls for particular precautions : a substance administered directly into the circulation cannot be removed once injected.
What is the difference between intradermal, subcutaneous and intramuscular injection ?
The essential difference lies in the injection depth and the tissue targeted.
An intradermal injection remains within the thickness of the skin. A subcutaneous injection passes through the dermis to reach the subcutaneous tissue. An intramuscular injection is performed more deeply to reach the muscle.
This difference in depth influences, in particular, the quantity that can be administered, the product’s diffusion and its absorption rate.
However, depth is not determined solely by needle length. It also depends on the insertion angle, anatomical region, tissue thickness and technique used.
What is an intra-articular injection ?
An intra-articular injection involves administering a product directly into a joint.
This route is used particularly in certain joint conditions to administer treatments locally. Depending on the indication, these may include corticosteroids or certain hyaluronic acid preparations, for example.
Injectable hyaluronic acid is therefore not used exclusively in aesthetic medicine. Some formulations are intended for joint indications and have specific characteristics.
An injectable product cannot be used indiscriminately in different tissues : its formulation, indication and authorised use must be respected.
What types of injections are used in aesthetic medicine ?
In aesthetic medicine, injections can be performed at different depths : intradermal, subcutaneous, intramuscular or in a deep plane in contact with the periosteum. The choice of injection plane depends on the product used, the anatomical area and the desired effect.
Botulinum toxin is most often injected into the muscle or immediately adjacent to the targeted muscle. The depth therefore varies according to tissue thickness and the location of the treated muscle. Some facial muscles are very superficial, while others lie in deeper planes.
Hyaluronic acid can be injected at several depths. An intradermal or superficial subcutaneous injection may be used for certain superficial corrections. Depositing product in the subcutaneous tissue can act on certain volumes and contours. For some structural corrections, such as the chin or certain cheekbone areas, the product may be placed much deeper, in a supraperiosteal plane, meaning just above the bone. The chosen plane also depends on the gel’s properties : not all hyaluronic acids are designed to be injected at the same depth.
Skinboosters are generally injected into the deep dermis or at the dermal-hypodermal junction, according to the product and technique used. Their main aim is to improve certain skin properties, particularly hydration and quality, without seeking the projection achieved with some fillers.
Mesotherapy involves much more superficial injections. Very small quantities of product are deposited through multiple intradermal injections, in the superficial or middle layers of the dermis according to the technique used.
Collagen stimulators are placed more deeply than mesotherapy. However, their injection plane depends directly on the product. Some are injected into the subcutaneous plane, while others may be deposited in deeper planes. They must not be injected indiscriminately at every depth : their formulation and indications determine the appropriate plane.
There is therefore no standard « aesthetic injection depth ». From superficial to deep, the product may be deposited in the dermis, at the dermal-hypodermal junction, in subcutaneous tissue, at muscle level or in a deep supraperiosteal plane. The choice of depth determines both the effect achieved and treatment safety.
At what depth are facial injections performed ?
There is no standard depth applicable to the entire face.
The skin and underlying tissues are not the same thickness at the forehead, temples, lips, cheeks or chin. Beneath the skin are also different fat compartments, muscles, vessels, nerves and the bony plane.
Depending on the treatment, the doctor may seek a very superficial plane or, conversely, position the product much deeper.
For a hyaluronic acid injection, for example, depth is determined by the desired effect and the gel’s rheological characteristics. A product intended to improve certain skin characteristics is not necessarily injected into the same plane as a gel used to provide structural support to the chin or cheekbones.
Knowledge of anatomy is therefore inseparable from product selection.
Needle or cannula : what is the difference when performing an injection ?
An injection can be performed using a needle or, for certain procedures, a blunt-tipped cannula.
The needle has a sharp tip and allows small quantities of product to be deposited precisely.
The cannula generally has a blunt tip and a side opening. It is introduced through a previously created entry point and can allow a larger area to be treated through a limited number of access points.
The choice between needle and cannula does not depend solely on the doctor’s preferences. It is determined by the anatomical area, product, intended plane and technique used.
Both instruments have specific advantages, limitations and risks.
Why is injection depth important ?
Depth directly determines the tissue in which the product is deposited.
A product intended for the dermis will not necessarily produce the same effect if placed in a much deeper plane. Conversely, some products intended to provide structural support are not designed for superficial injection.
In aesthetic medicine, the choice of injection plane therefore influences both the result and the safety of the procedure.
The face has complex vascular anatomy. Certain areas contain vessels that may be injured or, with some fillers, accidentally injected.
A facial injection therefore involves more than choosing a product : it requires determining what to inject, where to inject it and in which anatomical plane to place it.
What are the risks of an injection ?
The risks depend on the injection type, the product administered and the anatomical region concerned.
The most common local effects include temporary pain, redness, swelling or bruising at the injection site. Infection is possible whenever the skin barrier is broken, although aseptic measures aim to reduce this risk.
Other complications are specific to the product and technique used.
With facial fillers, some vascular complications are rare but potentially serious. These explain the importance of precise knowledge of facial anatomy, choosing the injection plane and promptly managing any complication.
How do you choose the appropriate type of injection ?
The choice of an injection is based first on the medical indication and the product to be administered. It is not a matter of arbitrarily choosing between an intradermal, subcutaneous or intramuscular injection.
In aesthetic medicine, the reasoning is even more anatomical. A superficial wrinkle, impaired skin quality, muscle contraction and volume loss do not involve the same mechanism and therefore do not require the same treatment.
The consultation identifies the structure responsible for the observed change before determining the appropriate product, technique and injection plane.
In Geneva, this preliminary analysis allows a strategy to be chosen that suits the patient’s anatomy and the intended objective.
Article written by Dr Valeria Romano
Dr Valeria Romano supports each patient through a comprehensive approach to facial, body and intimate aesthetics, as well as skin and hair quality. Every treatment is based on a personalised medical assessment.
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