ARE THERE ANY SIDE EFFECTS TO AESTHETIC INJECTIONS ?

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Aesthetic injections – hyaluronic acid, botulinum toxin, Sculptra, Skinboosters – are today among the most commonly performed medical procedures for aesthetic purposes, both for their effectiveness and their non-invasive nature. When well executed, they offer harmonious, natural, and reversible results.
However, like any medical procedure, they are not free from possible side effects. While the vast majority are mild, transient, and harmless, some effects may require monitoring, or even specific medical management. It is therefore essential that the patient is fully informed, and that the doctor practices with the utmost rigor, within a framework compliant with safety standards.

What is the difference between a side effect and a complication ?

It is essential to distinguish between a side effect and a complication, two concepts that are sometimes confused. A side effect is an expected or predictable response of the body to a product or medical procedure: it is generally mild, transient, and known to the doctor. For example, slight swelling after an injection is a typical side effect.
A complication, on the other hand, occurs unexpectedly, abnormally, or excessively. It may result from an incorrect indication, a technical error, or an unpredictable individual reaction. Managing a complication often requires close medical follow-up, or even specific treatment.
Understanding this distinction helps to better grasp the normal aftermath of an injection and not confuse an expected reaction with a genuine medical problem.

Common, mild, and transient side effects of injections

Most of the side effects observed after an aesthetic injection are part of the body’s normal response to skin penetration and do not constitute complications.

Bruises and hematomas : these are the most frequent side effects. The needle or cannula may damage a small capillary vessel and cause a local bruise. This disappears spontaneously within a few days, without the need for treatment. Simple precautions, such as avoiding aspirin, anti-inflammatory drugs, or certain dietary supplements before the injection, can help reduce this risk.
Redness, swelling, local tenderness : slight swelling (edema) or redness at the injection site is normal, especially in areas where the skin is thin, such as the lips or under-eye area. These signs disappear within 24 to 72 hours, sometimes more quickly. They can be alleviated by applying local cold, and do not require specific treatment unless they persist.
Sensation of tightness or foreign body : some patients describe an unusual feeling in the injected area, especially after a volumizing filler. This sensation is transient and generally disappears within one to two weeks, as the product integrates harmoniously with the tissue.

Moderate or delayed side effects

Asymmetry or overcorrection : asymmetry may result from an uneven injection or from a different tissue response on one side of the face compared to the other. Overcorrection, on the other hand, occurs when the amount of product exceeds what is aesthetically necessary. These imbalances are generally easy to correct with a small adjustment during a touch-up; or, in the case of excess hyaluronic acid, by injecting hyaluronidase, an enzyme that breaks down the excess gel.
Subcutaneous nodules : sometimes, especially in mobile areas or where the skin is thin, small indurations may form under the skin. They correspond to localized accumulations of product, often poorly distributed or injected too superficially. These nodules are most often painless and transient, but should be monitored. In case of persistence, targeted massage or dissolution may be considered.
Delayed inflammatory reactions : more rarely, patients may develop a localized or diffuse inflammatory reaction, several weeks or even months after the injection. These reactions are most often mild, but can appear striking: swelling, redness, discomfort. They may be triggered by an intercurrent viral infection (flu, COVID), an immune stress (vaccination, autoimmune reaction), or a poorly tolerated product. In such cases, appropriate medical management, sometimes with local anti-inflammatory or corticosteroid treatment, is sufficient.

Rare but serious complications

Vascular embolism : the most feared complication – although rare – is vascular embolism. It occurs when the injected product accidentally enters a blood vessel, blocking local circulation. This can lead to skin necrosis, or even irreversible blindness if a periocular artery is affected. These exceptional cases justify that injections be performed exclusively by doctors trained in the vascular anatomy of the face, capable of acting immediately: injection of hyaluronidase, vascular massage, local anticoagulation.
Infection : toute effraction cutanée comporte un risque infectieux, même minime. Si les règles d’asepsie médicale stricte sont respectées, ce risque est quasi nul. En revanche, les injections pratiquées en dehors du cadre médical, dans des conditions d’hygiène douteuses, exposent à des cellulites, abcès ou infections bactériennes retardées parfois graves.

Side effects specific to botulinum toxin

Botulinum toxin, although different from fillers, can also cause certain side effects, generally mild and transient :

Ptosis (drooping of the eyelid) : caused by the unintentional diffusion of the product to an adjacent muscle. The effect is temporary, but may last for a few weeks.
Asymmetry of the smile or drooping eyebrow : linked to an uneven distribution of the toxin.
Headaches or frontal tension in the days following the injection, often related to muscular adaptation.

All these effects disappear with the elimination of the product, without aftereffects.

Product traceability : an essential safety measure to prevent adverse effects

A factor often overlooked in the prevention of side effects is the quality and traceability of the injected products. Poorly stored hyaluronic acid, an unauthorized or counterfeit product, or incorrectly dosed botulinum toxin may induce unexpected reactions, which are more frequent and more difficult to treat.
This is why any serious doctor uses only CE-marked products or those approved by Swissmedic, keeps complete traceability (batch, manufacturer, date of injection), and provides the patient with a traceability label of the product used.

Who is most at risk of side effects ?

Certain patient profiles are more likely to experience adverse effects :

People with autoimmune or chronic inflammatory diseases.
People who have previously had allergic reactions to an injectable product.
Patients injected by non-doctors.
People who have received multiple injections of different products within a short period of time, without an overall strategy.

These situations justify a thorough medical evaluation and increased caution in indications.

Side effects according to the injected area

Not all areas of the face carry the same risk of side effects. Some are more vascularized, more sensitive, or more mobile, which can influence the type and frequency of reactions observed.

Lips : prone to post-injection swelling, sometimes striking, due to their rich vascularization and constant mobility.
Under-eye area : a delicate zone, poorly vascularized, with thin skin. Poorly chosen or improperly injected hyaluronic acid can cause a Tyndall effect (bluish reflection under the skin), visible irregularities, or persistent water retention.
Nose : a high vascular risk area. Any injection in this region must be performed with extreme caution to avoid a severe complication (necrosis or embolism).
Nasolabial folds and marionette lines : areas prone to small surface irregularities in case of overcorrection or too superficial injection. There is also a risk of vascular occlusion and therefore necrosis.

Adapting the choice of product, injection technique, and depth according to the treated area is essential to limit adverse effects.

The role of injection technique in the occurrence of side effects

The occurrence of side effects depends greatly on the technique used by the doctor. Several factors influence the risk :

Type of instrument : needle or cannula. The cannula is often preferred to reduce bruising and avoid injection into a blood vessel. Its use is mandatory in areas with vascular risk.
Injection depth : an injection that is too superficial can create visible irregularities, while an injection that is too deep may be ineffective, meaning the result will not be visible.
Injection speed : in inexperienced hands, an injection performed too quickly (relative to the rate of product introduction) can cause swelling, exaggerated inflammation, or poor product distribution.

The doctor’s experience and knowledge of anatomy are therefore crucial to avoid technical side effects, even when the product is perfectly tolerated by the patient.

Is it possible to develop an intolerance or allergy to injected products ?

Allergic reactions to modern filler products are extremely rare, particularly because the substances used – such as hyaluronic acid – are biodegradable, biocompatible, and very similar to those naturally produced by the body.
However, in very rare cases, one may observe :

A delayed immune reaction (localized chronic inflammation, persistent redness).
Hypersensitivity to certain accessory components, such as cross-linking agents or preservatives.

These exceptional cases are managed by a competent doctor using anti-inflammatory or enzymatic treatments. It is therefore essential that the injection be preceded by a thorough medical consultation, especially in patients with immune disorders or a history of allergies.

Article written by Dr Romano Valeria

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