Neuromodulator Complications & How to Avoid Them

Reducing Risk = Producing Reward. A simple equation!

Most recent data would suggest that Botulinum toxin injections are the most common cosmetic procedure performed in the world, with an estimated 3 million injections per year (Witmanowski & Błochowiak, 2020). As such, the effects of botox injections and its other brand counterparts have been vastly studied in recent years, and it has been found that related complications and adverse events are rare and often tend to be transitory and short in duration. Nevertheless, understanding potential complications and what can be done to minimize them can still be essential to providing quality service to those seeking treatment, and will continue to promote the healthy growth of the field. 


Most complications from cosmetic BoNT-A procedures are well-localized, reversible, and self-limited, developing within a few days of the injection, and usually disappearing without any additional treatment (Witmanowski & Błochowiak, 2020). Events are usually related to injection site injury, which can be minimized with several precautions and categorized into the following:

Bruising (Ecchymosis or Hematoma)

Bruising results from injuring a blood vessel at the site of the injection as the treated areas are fully vascularized. Bruising affects 11%-15% of patients and most commonly occurs in the ocular area (Witmanowski & Błochowiak, 2020). To minimize or prevent bruising, practitioners should check if patients are using any drugs, medicines, or vitamins that change coagulation. Applying cold pads or ice packs before the injections, firm local compression immediately after the injection, and intense pulsed light or other light-based devices may be useful to minimize the ecchymosis or hematoma, especially at the inferior lid (da Cunha, da Cunha & Tamura, 2017).

Localized Pain

Localized pain is associated with the puncturing of skin by the needle. To reduce injection site pain, topical anesthetic creams can be used, but most important is the use of a correctly sized needle and safe techniques, such as having the needle bevel up and injecting slowly. Pain can also be minimized by using a preservative containing saline solution to dilute the botulinum toxin, specifically one with a higher pH. Dry skin and flakiness can occur in some patients, likely due to decreased sweat gland activity in the area. 


Infection is rare and prevention highly effective, by ensuring the area is properly cleaned with an antiseptic solution, removing all makeup residue among any other contaminants. The practitioner should employ aseptic technique when administering the treatment, and afterward the patient should be instructed to not touch the area or apply makeup for at least 6 hours until the open injection sites are healed. If an infection occurs, a course of antibiotics and close monitoring of the area is essential to ensure that an abscess does not form, which could potentially result in a scar.


Headaches can be rather common (but short-term) after treatment and occur due to several potential reasons including the BoNT-A causing muscle spasm, the needle hitting the periosteum, deep muscle hematomas, or general irritation from facial injection. Most headaches, occurring in approximately 16% of patients receiving treatment for glabellar lines (da Cunha, da Cunha & Tamura, 2017), are mild and resolve a few days after treatment. There have been reports of more severe headaches lasting 2-4 weeks which can be treated with nonsteroidal anti-inflammatory drugs. 

More rare effects such as paresthesia, dysesthesia, hypoesthesia, or mild flu-like malaise and dry mouth may be related to nerve trauma and occur more commonly in non-cosmetic treatment, such as for rosacea. 

Allergic Reactions

Allergic reactions caused by botulinum toxin can cause a variety of symptoms, including edema, erythema or redness limited to the site of injection, through diffuse erythema, and generalized urticaria, to anaphylactic shock. Edema is usually related to the volume of the injected solution, i.e., dilution with more than 1 mL of saline (da Cunha, da Cunha & Tamura, 2017). An allergic reaction is more likely to affect patients receiving frequent and premature touch-ups, and occur a few minutes after the injection, if at all. In the rare case of anaphylactic reaction, treatment with an adrenaline injection and continual monitoring of the patient should be implemented. To help prevent possible allergic reactions, the practitioner should be well acquainted with the patient’s medical history, and practice extra caution with patients with multiple, pre-existing allergies as they are at higher risk of being allergic to botulinum toxin (Witmanowski & Błochowiak, 2020).

More Severe Complications

The frequency of serious side effects is 33 times higher for therapeutic than for cosmetic uses, as therapeutic treatments implement a higher dosage – the cosmetic use of botulinum toxin rarely causes severe side effects. One of the most feared complications after BoNT-A treatment is undesirable motor muscle impairment, as it directly affects the quality of life of the patient, as well as the aesthetic results. Visually noticeable complications include eyebrow ptosis (most frequently), eyelid ptosis, exacerbation of the infraorbital or nasojugal sulcus pads, facial asymmetries and general changes to the patient’s smile, food retention issues, chin herniation, weakness of the masticatory function, and speech difficulties. Most frequently these complications are associated with an inadequate understanding of the patient’s individual facial anatomy, causing the injection of BoNT-A into the wrong muscle, incorrect dosage, excess saline dilution, a lack of familiarity with the chosen toxin, and diffusion of the toxin past the intended injection site. Proper, continued training and individualized knowledge of the patient are paramount in avoiding these complications. 

This wide spectrum of symptoms associated with muscle weakness or paralysis, dysarthria, dysphonia, dysphagia and respiratory arrest is known as botulism (Witmanowski & Błochowiak, 2020). Evidence of mild botulism can appear as severe and long-lasting headache and fatigue. Reports show that up to 1% of patients who receive botulinum toxin injections may experience these symptoms, and that they can occur a few years after continued injections even if the patient never showed symptoms of botulism upon prior injections. 

Until additional evidence supporting the safe use of botulinum toxin during pregnancy and nursing is presented, pregnant women and nursing mothers should not be treated. Because of a higher risk of undiagnosed medical and neurologic disorders, and higher therapeutic drug intake, aesthetic botulinum toxin application in patients older than 75 years is also controversial (Witmanowski & Błochowiak, 2020). 

It is also important to note that the majority of studies done on BoNT-A complications are for cosmetic treatment for the lines of the upper third of the face, and not the medium and inferior third as those uses are still considered off-label. Even more importantly, studies on complication and safety ratings of BoNT-A injections have not solely focused on non-medical professional administrators, who administer a significant portion of injections to the public, and therefore a bias may be present in the data; “Adverse event rates are shown to be higher when BoNT-A is injected by inexperienced practitioners without sufficient knowledge of anatomy. This practitioner factor effect on the prevalence of adverse events has not been well studied, and it is an important area for further study” (Zargaran et al., 2022). 

Studies show that cosmetic BoNT-A injections appear safe, especially in the glabellar and forehead area, and most complications are rare, mild and transient – though they can affect the quality of life of the patient beyond a physical experience. Extensive knowledge of anatomy, including the individualized anatomy of the patient, are essential, as well as upkeep on best practices pertaining to techniques and specific BoNT-A brands. As most severe reactions in cosmetic treatment are associated with incorrect and overly frequent dosage, intervals between the injections should be kept to a minimum of at least 3 months and frequent touch-ups should be avoided. Studies to date lack some consistency when defining treatment related complications and also lack detail on the practitioner profile, which are important areas for further study to uphold the highest standards of patient safety in this rapidly expanding field (Zargaran et al., 2022).


Witmanowski H, Błochowiak K. The whole truth about botulinum toxin – a review. Postepy Dermatol Alergol. 2020 Dec;37(6):853-861. doi: 10.5114/ada.2019.82795. Epub 2019 Feb 5. PMID: 33603602; PMCID: PMC7874868.

da Cunha M.G., da Cunha A.L.G., Tamura B.M., Botulinum Toxin: Complications and Their Management. Springer International Publishing AG 2017. Clinical Approaches and Procedures in Cosmetic Dermatology 4, 

David Zargaran, MBBS, BSc (Hons), AICSM, MRCS, Florence Zoller, MD, Alexander Zargaran, MBBS, BSc (Hons), PGCert (Ed), MRCS, Eqram Rahman, MBBS, MS, MMEd, PhD, Alexander Woollard, BM, BSc, PhD, FRCS (Plast), Tim Weyrich, MSc, PhD, Afshin Mosahebi, MBBS, FRCS, FRCS (Plast), PhD, MBA, Complications of Cosmetic Botulinum Toxin A Injections to the Upper Face: A Systematic Review and Meta-Analysis, Aesthetic Surgery Journal, Volume 42, Issue 5, May 2022, Pages NP327–NP336,


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