Botulinum toxin injections, commonly known as Botox®, are today one of the most effective and safest treatments to combat localized hyperhidrosis. By temporarily blocking the stimulation of the sweat glands, they significantly reduce sweat production in targeted areas such as the underarms, hands, feet, or face. However, like any medical procedure, this treatment is not free from side effects. Although the tolerance profile of Botox is excellent, it is essential to be aware of its potential side effects.
The Botox used against hyperhidrosis is injected in a very superficial manner, into the dermis, close to the eccrine sweat glands. Unlike its use in neurology, the doses injected in this context are low, which considerably limits the risk of systemic side effects.
The possible adverse effects are therefore essentially local, temporary, and most often mild, provided that the treatment is performed by an experienced physician and in a proper medical setting.
It is common to observe after the injection certain moderate skin signs, which generally do not require any specific treatment. Among them :
These local reactions are perfectly normal and are due to an inflammatory response related to the injection itself. They do not indicate an intolerance to the product.
Certain anatomical areas are more sensitive than others to the action of botulinum toxin. That is why a thorough knowledge of functional anatomy is essential to minimize the risk of specific adverse effects.
The axillary area is the one where the treatment is the safest and best tolerated. Side effects are rare and generally mild: feeling of skin tightness or excessive dryness in the days following the injection; minor residual pain at the needle entry points; local hypersensitivity to touch or friction. No motor impairment is to be feared in this area.
Treatment of the hands is technically more delicate and may be accompanied by transient side effects. In 5 to 10% of cases, moderate muscle weakness may occur, mainly affecting the thumb or the intrinsic muscles of the hand. This impairment can cause temporary difficulty with fine grip (writing, handling objects), but it remains reversible within a few weeks. A feeling of stiffness or tension may also appear in the days following the injection.
These adverse effects are related to partial diffusion of the toxin to adjacent muscles and are most often well tolerated.
Tolerance of plantar treatment is comparable to that observed in the hands, although injections are generally more uncomfortable. Possible side effects include post-procedure pain during the first 24 to 48 hours, a transient sensation of imbalance or change in plantar support, as well as small bruises. Prior local anesthesia is recommended to improve patient comfort and limit post-injection adverse effects.
Treatment of the face requires particular technical precision. The main risk lies in inappropriate diffusion of the toxin, which may cause temporary asymmetry of facial expression (eyebrow ptosis or slight eyelid droop) if the injection is too close to the orbicular or frontal muscles. Other adverse effects may include a pulling sensation in the forehead or temporal region, as well as eye dryness if injected near the peri-orbital area.
These side effects are rare and completely reversible within a few weeks.
Systemic diffusion of botulinum toxin in the context of treating localized hyperhidrosis is considered extremely unlikely, given the low doses administered and the strictly superficial location of the injections.
However, in very rare cases (< 1 %), transient effects may occur :
True allergic reactions to botulinum toxin are exceptional, but may manifest as :
A precise medical history is essential to identify any history of allergy or abnormal reaction to a previous treatment.
Contrary to some misconceptions, treatment of hyperhidrosis with Botox does not cause any physiological tolerance or dependence. However, the significant improvement in quality of life can create a high psychological expectation, leading some patients to request sessions more frequently. This remains an understandable request, but the physician must ensure that the interval between sessions is respected (on average 5-6 months) to avoid the development of neutralizing antibodies.
There is also no rebound effect: sweating gradually returns to the same level as before the treatment, without sudden exacerbation.
Annual, or even semi-annual, repetition of botulinum toxin injections is entirely feasible and does not involve any risk of tolerance or cumulative toxicity, provided that the treatment is performed according to best medical practices.
On the contrary, some patients report prolonged improvement: over time, the intensity of sweating tends to decrease more durably, the interval between sessions can lengthen, and the body seems to “relearn” a more physiological sweating threshold.
Botulinum toxin does not cause permanent changes to the nerves, but a lasting regulation of sweat secretion has been observed in patients treated regularly over several years.
The only precaution is to respect the recommended medical dosages and to entrust the injections to an experienced physician. To date, no long-term contraindications have been identified, apart from preexisting neuromuscular disorders.
Allergic reactions to botulinum toxin are extremely rare, but as with any injected medication, they can never be completely ruled out. Verified cases of hypersensitivity generally involve one of the product’s excipients (such as stabilizing human albumin), and not the botulinum toxin itself.
Possible manifestations, although very uncommon, may include :
In practice, the physician must ask the patient about any history of severe allergies, monitor the injection in a safe environment, and have emergency equipment available. An intradermal test is not routinely necessary, except if a previous allergy suspicion has been documented.
In the majority of cases, Botox begins to take effect between 3 and 7 days, with maximal effect reached around 15 days after the injection. The average duration of efficacy is 4 to 6 months, depending on the treated area, the severity of hyperhidrosis, and the individual patient’s response. However, sometimes sweating may reappear sooner, around the 3rd or 4th month, or the effect may be incomplete.
In these situations, several causes can be considered :
The treatment most often consists of a targeted touch-up session, after precise assessment of the affected area. However, it is not recommended to perform a too early or identical reinjection, to avoid any risk of cumulative overdose. The protocol is then progressively and individually adjusted in subsequent sessions.
No, it has not been shown that side effects intensify with repeated botulinum toxin injections, provided that doses are respected and intervals are sufficiently spaced (at least 4 to 6 months).
On the contrary, the majority of patients report increasingly satisfactory tolerance over successive sessions. This progressive improvement can be explained by several factors. On one hand, the skin tends to become less sensitive to repeated punctures. On the other hand, over the course of treatments, the physician refines their knowledge of the patient’s specific anatomy, allowing for more precise targeting of the involved muscles or sweat glands. Finally, protocols are progressively adjusted based on individual response, which helps optimize both comfort and clinical results.
The only side effect potentially related to too frequent use is the development of neutralizing anti-botulinum toxin antibodies, which may gradually reduce treatment efficacy. This phenomenon remains exceptional, especially at the doses used for hyperhidrosis, and can be avoided by respecting a minimal interval between sessions.
Botox acts exclusively locally when used for the treatment of hyperhidrosis. At the recommended therapeutic concentration, it does not diffuse systemically, which rules out any risk of generalized suppression of sweating. This specificity clearly distinguishes it from more invasive interventions, such as thoracic sympathectomy, which can lead to notable side effects, such as compensatory sweating in distant areas.
With Botox, there is no compensatory phenomenon: the body does not attempt to sweat more in other areas to offset the localized block. The effect remains strictly limited to the injected area, without affecting the function of other skin regions. This precision of action is a key therapeutic advantage. It allows for effective targeting of the responsible sweat glands while preserving the body’s overall thermoregulation.
The treatment is both safe, effective, and well tolerated.
Simultaneous treatment of multiple areas of the body is possible, but it requires a careful evaluation. In theory, the cumulative doses injected increase the potential risk of systemic diffusion, but in practice, this risk remains extremely low as long as the physician respects the recommended maximum dosage.
The physician precisely assesses the total dose to be administered, taking into account the type of botulinum toxin used—whether Botox®, Xeomin®, or Dysport®. This personalized estimation aims to avoid any risk of overdose, particularly in patients with low body weight. When the area to be treated is extensive or multiple zones are involved, it may be appropriate to perform the injections in two stages. For example, the palms can be treated first, followed by the underarms a week later, to optimize tolerance and treatment efficacy. Side effects are not more frequent when treating multiple areas simultaneously, but local tolerance (pain, tension, stiffness) may vary depending on the region. Combined treatment must be strictly personalized to ensure both therapeutic efficacy and pharmacological safety.
The prevention of adverse effects related to botulinum toxin injections relies on several fundamental elements. It begins with the physician’s expertise, who must have rigorous training and a thorough knowledge of the functional anatomy of the area to be treated. Strict adherence to the recommended doses for each location, as well as precise injection technique—using small doses evenly distributed—are also essential to ensure safety and efficacy.
In the hours following the procedure, patient compliance with post-treatment instructions is important. It is strongly advised to avoid intense physical activity, heat exposure such as saunas, or massages during the first 24 hours. The injected area should not be manipulated. Finally, any unusual reaction or persistent side effect should be reported immediately to the physician.
Article written by Dr Romano Valeria
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