Botulinum toxin injections: advantages and disadvantages.

Originally, botulinum toxin was used exclusively in medicine to manage certain neurological or muscular disorders. The term "botox", which initially referred to a trademark, has gradually become the generic term for botulinum toxin injections. This substance, produced by the bacterium Clostridium botulinum, is known for its toxicity at high doses, but also for its therapeutic effects at extremely low doses.

Botulinum toxin must be purified, accurately dosed and administered under strictly controlled conditions to guarantee its safety. Injections should be performed exclusively by trained professionals in appropriately equipped medical facilities.

First authorised for aesthetic purposes in the late 1990s, and used in France since the early 2000s, Botox is today primarily used to soften expression lines. Its mechanism of action is based on blocking the release of acetylcholine, a neurotransmitter involved in muscle contraction. By preventing this nerve transmission, the targeted muscle gradually relaxes, limiting the contractions responsible for the formation or deepening of wrinkles. Injections are most commonly performed on the glabellar lines, forehead wrinkles, crow’s feet and nasolabial folds. The effects are not immediate: they typically appear between 3 and 7 days after injection and wane after 4 to 6 months.

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If Botox injections are so widely practised today, it is because they provide visible benefits, particularly for expression lines. By acting directly on the muscle activity responsible for repeated facial contractions, botulinum toxin enables the smoothing of certain existing wrinkles and helps prevent the deepening of those that are forming.

Botox injections also have the advantage of being simple and quick procedures. The procedure generally takes only a few minutes and requires neither general anaesthesia nor prolonged social isolation. The injections are performed using very fine needles, making the process minimally painful for most patients. Post-treatment effects are generally mild, with only slight redness or transient bruising at the injection site.

These characteristics partly account for the success of Botox, which offers a gradual aesthetic improvement, with a relatively mild protocol when administered by an experienced professional.

Botox injections are generally regarded as safe when performed under appropriate conditions, yet they are not entirely free of adverse effects. The most frequent complications are mild and transient, occurring in the days following the injection. They chiefly involve the injection site, presenting as pain, redness, swelling, bruising or local tenderness. Headaches or flu-like sensations may also be reported. At the muscular level, excessive or poorly targeted relaxation can lead to undesirable aesthetic outcomes, such as facial asymmetry, a frozen appearance or drooping of the eyelid or eyebrow (ptosis). While many of these manifestations typically resolve within a few days to weeks without specific intervention, some require corrective injections.

Cutaneous or allergic reactions have also been reported, albeit less frequently. They may present as diffuse redness, itching, skin eruptions, urticaria or facial swelling. In very rare cases, delayed hypersensitivity reactions have been described. One case study, in particular, reported a delayed hypersensitivity reaction following injections of botulinum toxin. In one patient, the initial injection performed in July 2019 yielded aesthetic results deemed insufficient after one month (A). A touch-up injection was then administered (B). Four days after this second injection, the patient developed marked facial oedema accompanied by erythematous lesions, indicating a delayed inflammatory reaction (C). The lesions resolved spontaneously after three weeks.

Less commonly, serious complications may be observed after injections of botulinum toxin. They are most often linked to excessive spread of the toxin beyond the originally targeted injection site, to the administration of overly high doses or to an inappropriate injection technique. As botulinum toxin acts on neuromuscular transmission, even limited systemic spread can disrupt essential muscle functions. Such events remain exceptional in aesthetic medicine but are well documented in the medical literature.

Among the reported manifestations are general symptoms suggestive of a clinical picture resembling botulism. Patients may present with diffuse muscle weakness, marked fatigue, difficulty swallowing (dysphagia) or speaking (dysarthria). In the most severe cases, the respiratory muscles may be affected, leading to respiratory distress requiring urgent medical care. These effects are more frequently described during the therapeutic use of botulinum toxin, which involves higher doses, but have also been reported, albeit exceptionally, after aesthetic injections.

Ocular complications constitute another rare but specific risk of injections performed in the peri-orbital region. Diffusion of the toxin to the extraocular muscles or eyelids can result in double vision, drooping of the eyelid, severe ocular dryness or incomplete eye closure. The latter can expose the cornea to excessive drying, with a risk of irritation or, more rarely, corneal lesions. These complications underline the importance of precise anatomical knowledge and a rigorous technique when injecting into these sensitive areas.

In exceptionally rare cases, serious infectious or vascular complications have been reported, including deep soft-tissue infections or local vascular injuries. These events remain extremely uncommon and are often associated with inadequate aseptic conditions. Moreover, fatalities have been documented in the medical literature, primarily in therapeutic contexts involving high doses of botulinum toxin, especially in patients with significant comorbidities. In aesthetic medicine, such situations remain exceptional but justify clear patient information and strict adherence to clinical indications and safety protocols.

Botox injections are never a trivial procedure. In view of the possible, sometimes serious, adverse effects, it is essential to take the time to consider the decision carefully, to gather comprehensive information and to consult only a qualified and experienced healthcare professional who can assess the indications and contraindications and ensure the safety of the procedure.

• YIANNAKOPOULOU E. Serious and long-term adverse events associated with the therapeutic and cosmetic use of botulinum toxin. Pharmacology (2015).

• GRECO T. M. & al. Advanced techniques for the use of neurotoxins in non-surgical facial rejuvenation. Aesthetic Plastic Surgery (2020).

• RAHMAN A. & al. A review of complications due to the use of botulinum toxin A for cosmetic indications. Aesthetic Plastic Surgery (2021).

• GOLDUST M. & al. Complications of botulinum toxin A: An update review. Journal of Cosmetic Dermatology (2021).

• SCHIUMA A. T. & al. A systematic review and comparative analysis of botox treatment in aesthetic and therapeutic applications: Advantages, disadvantages, and patient outcomes. Cureus (2024).

• CHEN J. & al. Dysphagia and muscle weakness caused by botulinum toxin poisoning after cosmetic injection: Three case reports and clinical warnings. Dysphagia (2025).

• CAI H. & al. A rare case of delayed-onset hypersensitivity reaction and complete secondary treatment failure following repeated cosmetic botulinum toxin type A injections. Journal of Cosmetic Dermatology (2025).