Botulinum Neurotoxin Type A in Aesthetics: Notes for its clinical use.

Botulinum neurotoxin type A injection is the most common cosmetic procedure to correct facial wrinkles.

There are several brands that market botulinum neurotoxin type A. Despite decades of research supporting its safety and efficacy, the various brands tout differences in their results. Clinical trials provide a variety of data on these products, which may influence the decisions of consumers and professionals.

“…different brands promote differences in their results…”

In this post we would like to summarize and synthesize an interesting article that explains different aspects of botulinum neurotoxin type A that can help clinicians in clinical practice and patients to better understand botulinum neurotoxin.

In vitro analysis has shown that neuronal uptake of the toxin takes approximately 5 to 10 minutes after the toxin molecules reach the presynaptic membrane surface. The onset of paralysis usually manifests within 48 hours and usually lasts 4 to 5 months, although some patients show a shorter or longer onset of paresis and/or duration of effect. With continued cellular turnover in the NMJ, contractile function begins to return after several weeks, generally reaching pre-treatment strength in approximately 6 months.

“…repeated botulinum neurotoxin type A injections may result in slower functional recovery…”

Recovery of neuromuscular transmission requires the proliferation of motor axon sprouts to form new synaptic contacts at the motor endplate. There is evidence that repeated injections of botulinum neurotoxin type A may result in slower functional recovery.

Although all type A toxins have the same mechanism of action, clinical differences may arise. The speed and degree of reaction depend on both the concentration of the toxin and the density of the receptors.

The clinical effect depends on:

  1. External factors: Toxin concentration: Molecular potency.
  2. internal factors, such as the density of the receivers, which may vary according to:
    • muscle type,
    • muscle mass,
    • gender,
    • age and
    • Race and ethnicity.

What is the Molecular Potency of Toxin?

La potencia molecular del de la neurotoxina botulínica de tipo A, se relaciona con la cantidad de proteína neurotóxica (concentración de toxina) activa de 150 kDa (tamaño de la molécula) en la solución. It is only this protein that produces clinical effects. The different commercial formulations of botulinum neurotoxin type A have different molecular potencies measured in “units” that are not interchangeable between products. Tests and diluents vary between products, which may affect potency. Differences in the amount of neurotoxin have been demonstrated in different products.

The more botulinum neurotoxin type A, the sooner it begins to act and the longer it lasts.

Muscle Mass and Botulinum Toxin

Skeletal muscles, anchored to bones, differ markedly from the muscles of facial expression. The latter, together with soft tissues and skin, are responsible for the dynamic wrinkles that emerge with their contraction. Unlike the more defined skeletal muscles, facial muscles have interlocking and overlapping boundaries, and their superficial identification is challenging. These muscles work in pairs, providing varied expressions.

“…thicker and larger muscles may require higher and more frequent doses….”

Its mass differs significantly depending on the individual, gender and age. This variability influences the number and density of neuromuscular junctions, and therefore, the receptors for botulinum toxin type A. It is possible that there are genetic factors that determine these differences in neuromuscular receptors, as occurs in certain neuronal diseases.

“…An inadequate amount of toxin in a large muscle will not cause noticeable wrinkle relaxation…”

Correct dosing of botulinum neurotoxin type A is crucial. An insufficient dose in a large muscle will not alleviate wrinkles, while an overdose in less dense muscles may result in an excessively inert effect and risk of complications. Each muscle requires a unique dosing approach; for example, the orbicularis oculi will respond differently to the corrugator supercilii. The variability of contraction, even within the same muscle such as the frontalis, demands individualized attention.

“…the dosage of botulinum neurotoxin type A should be adapted considering the muscle mass…”

The dosage of botulinum neurotoxin type A should be adapted considering the muscle mass. Larger muscles such as the masseter may require larger and more repeated doses than smaller facial muscles.


Dosing of botulinum neurotoxin type A in men and women should consider differences in muscle mass. Men, who are increasing their demand for botulinum neurotoxin type A treatments, tend to require higher doses than women due to their greater amount and density of skeletal muscle, including facial musculature.

“…in men it is associated with a lower likelihood of response and generally require higher doses…”

This variability is accentuated by different facial expressions and expectations between genders. Therefore, when treating men, it is crucial to consider anatomical aspects and expectations, adjusting doses according to individual response.


The efficacy of botulinum neurotoxin type A is similar in different age groups in terms of response, duration and adverse events. However, dosages may vary due to changes in muscle mass and power with age. In particular, the muscles of the elderly are weaker and prone to atrophy, which may require less toxin to achieve results.

“…the elderly may require less dosage more frequently…”

However, their less elastic skin can complicate wrinkle correction. Thus, in the elderly, a cautious approach is suggested, opting for lower doses and more frequent touch-up treatments.

Race and ethnicity

Research on the aesthetic results of botulinum toxin type A in different racial and ethnic groups is limited. There are genetic and physical differences in the skin according to racial origin, which may influence the response to botulinum toxin type A.

“…Black patients may respond more intensely and Asian patients should be more conservative…”

One study showed that patients with skin of color showed a higher response rate to the certain neurotoxin at 30 days compared to white patients. It is crucial to consider these variations when treating different ethnicities, and in some cases, such as Asian patients, a more conservative approach to dosing is recommended.



Based on the above discussions, it is clear that there is no single dose of botulinum neurotoxin type A that is effective and safe for all patients. Therefore, it is recommended that physicians perform a thorough evaluation of each patient and adjust the dose according to the anatomical area being treated, muscle mass and strength, gender and age. In addition, patients should be reevaluated after administration of botulinum neurotoxin type A to determine the need for additional doses or readjustments in the future.

Clinical Efficacy

Although all botulinum neurotoxin type A products have been shown to be effective in reducing facial wrinkles, there are differences in clinical efficacy among the various products due to differences in the molecular structure and potency of the toxoid. Therefore, it is important for physicians to be familiar with the specific characteristics of each product and the recommended dosages to ensure optimal results.


Although adverse reactions to botulinum neurotoxin type A are rare, they can occur and are more likely with higher doses. The most common adverse reactions associated with the use of botulinum neurotoxin type A include pain at the injection site, hematoma, edema and eyelid ptosis. However, these reactions are generally mild and resolve on their own within a few days. To minimize the risk of adverse reactions, it is important that physicians follow dosing recommendations and administer the product accurately.

The use of botulinum toxin type A in aesthetic medicine has been shown to be effective and safe in the reduction of facial wrinkles. However, there are differences in efficacy and safety between different botulinum neurotoxin type A products, making product selection and proper dosing essential to ensure optimal results. When considering the use of botulinum neurotoxin type A in aesthetic medicine, it is important for physicians to be familiar with the specific characteristics of each product and the recommended dosages to ensure optimal results and minimize the risk of adverse reactions.