Botox in Underarms for Hyperhidrosis: Complete Guide
Botulinum toxin type A—marketed as Botox (Allergan) and Dysport (Galderma)—is the gold standard treatment for primary axillary hyperhidrosis. FDA-approved since 2004 specifically for this indication, it works by blocking the release of acetylcholine at the nerve endings that stimulate eccrine sweat glands, thereby reducing armpit sweat production significantly without affecting the body's overall thermoregulation. If you want to understand how botulinum toxin works at the molecular level, we recommend our dedicated guide.
In controlled clinical trials, between 50 and 55% of patients treated with onabotulinumtoxinA achieved an improvement of two or more points on the HDSS scale (Hyperhidrosis Disease Severity Scale) at four weeks, compared to only 6% with placebo. The reported satisfaction rate exceeds 90% and effects appear within the first week.
Summary
- What it is: intradermal injection of botulinum toxin in each underarm to block excessive sweating.
- Approved dosage: 50 units of Botox per underarm (100 U total), distributed across 10-15 injection points in a grid pattern.
- Duration of effect: 4 to 12 months, with an average of 7 months; repeated sessions can extend the result.
- Safety: compensatory sweating is reported in less than 6% of patients, well below the incidence associated with surgical sympathectomy (up to 70-98%).
- Evidence: FDA-approved (2004), EMA and various regulatory agencies (COFEPRIS, ANVISA, INVIMA) with level A evidence for axillary hyperhidrosis.
What is hyperhidrosis?
Hyperhidrosis is the production of sweat that exceeds what is necessary for body thermoregulation, to the point of interfering with daily activities. It affects approximately 3% of the general population, and the underarms are the most frequently affected area (up to 63% of cases), either in isolation or combined with other areas such as palms, soles, or face.
Primary vs. secondary hyperhidrosis
Primary (idiopathic) hyperhidrosis presents without an underlying medical cause. Its diagnostic criteria include: visible excessive sweating for at least six months, a bilateral and relatively symmetric pattern, onset before age 25, at least one episode per week, positive family history (present in about 35% of cases), and absence of night sweats. The average age of onset is around 14-15 years.
Secondary hyperhidrosis, on the other hand, has an identifiable cause: thyroid disorders, diabetes, menopause, infections, medications (antidepressants, opioids), or neurological conditions. Unlike primary hyperhidrosis, it can be unilateral, generalized, and accompanied by night sweats. Identifying this distinction is fundamental because secondary hyperhidrosis requires treating the underlying cause before addressing the symptom.
The HDSS scale: how severity is measured
The Hyperhidrosis Disease Severity Scale (HDSS) is the standard clinical tool for assessing severity. The patient selects the statement that best describes their experience:
- My sweating is never noticeable and never interferes with my daily activities.
- My sweating is tolerable but sometimes interferes with my daily activities.
- My sweating is barely tolerable and frequently interferes with my daily activities.
- My sweating is intolerable and always interferes with my daily activities.
A score of 3 or 4 indicates severe hyperhidrosis. A one-point improvement on the HDSS is associated with a 50% reduction in sweat production; a two-point improvement equals an 80% reduction. Almost two-thirds of patients seeking treatment present with HDSS scores of 3 or 4.
How does botox work for axillary hyperhidrosis?
Botulinum toxin blocks the release of acetylcholine at the neuroeffector junction of eccrine sweat glands. Unlike its cosmetic use—where it is injected into muscle to relax it—in axillary hyperhidrosis it is injected intradermally, directly into the skin layer where the sweat glands are located. The underlying muscle is not affected.
This blockade is temporary and reversible: the nerve endings regenerate their contact points with the glands in a process that takes between four and twelve months, explaining the need for maintenance sessions. With repeated sessions, evidence from longitudinal studies at four years suggests that the duration of effect can progressively extend.
Regulatory approval
The FDA approved onabotulinumtoxinA (Botox) for severe primary axillary hyperhidrosis in 2004, making it the first non-muscle indication approved for this molecule. Since then, multiple regulatory agencies have authorized it for this indication, including the EMA in Europe, COFEPRIS in Mexico, ANVISA in Brazil, and INVIMA in Colombia. The level of clinical evidence is A (effective, based on multiple class I and II studies).
The procedure step by step
A botox session for axillary hyperhidrosis lasts approximately 15 to 20 minutes and does not require general anesthesia. These are the steps:
1. Starch-iodine test (Minor's test)
Before any injection, the physician applies an iodine solution to the clean, dry skin of the underarm, followed by a thin layer of cornstarch. Areas with active sweating stain a dark blue-violet color within minutes, creating a precise visual map of the hyperhidrotic area. This test allows the physician to determine exactly where to inject and avoid wasting product outside the affected area. It is performed before any topical anesthesia, as this could alter the sweating pattern.
2. Grid pattern marking
Over the stained area, the physician draws a grid with injection points spaced 1 to 2 cm apart, generating a pattern of 10 to 15 points per underarm. The goal is to create anhydrotic halos (areas without sweating) that overlap with each other until the entire affected area is uniformly covered.
3. Intradermal injection
With a 30-gauge needle (very fine), 50 units of Botox per underarm (100 U total) are injected, distributed in aliquots of 0.1 to 0.2 mL per point. Each injection is applied at a depth of approximately 2 mm, with the needle at a 45° angle and bevel facing up to minimize leakage and ensure the product remains in the dermis. The complete session usually takes between 15 and 20 minutes.
Does it hurt?
Most patients describe the injections as a mild pinprick, comparable to a small pinch. The 30-gauge needle is one of the finest available. For those with high sensitivity, a topical anesthetic (such as tetracaine) or ice can be applied before the procedure, although many patients do not find this necessary.
Results and duration
The effect of botox in underarms is rapid: a noticeable reduction in sweating is perceived within the first 2 to 4 days, with progressive improvement until reaching maximum effect around two weeks.
How long does the effect last?
The average duration of effect is 6 to 7 months, with a documented range of 4 to 12 months depending on the patient. In a four-year longitudinal study with up to five sessions of 50 U per underarm, the median duration of each treatment ranged from 175 to 238 days (approximately 6 to 8 months). At least 22% of patients did not return to an HDSS of 3 or 4 one year after the first session, suggesting that some patients obtain a particularly long-lasting response.
Does it improve with repeated sessions?
Yes. Evidence suggests that the duration of effect may increase with consecutive treatments. This is likely due to gradual remodeling of nerve endings, although the exact mechanism is still being investigated. In clinical practice, many patients who initially needed retreatment at 5-6 months report longer intervals after two or three sessions.
Satisfaction rate
The reported satisfaction is consistently high. In the pivotal European study, 93% of patients treated with onabotulinumtoxinA declared themselves satisfied or very satisfied with the treatment during the 16-week follow-up period, compared to 30% of the placebo group.
Alternative treatments for hyperhidrosis
Botox is not the only option. The choice of treatment depends on severity, the affected area, patient preferences, and response to previous therapies. This table compares the main alternatives:
| Treatment | Mechanism | Efficacy | Duration | Invasiveness | Main adverse effects |
|---|---|---|---|---|---|
| Antiperspirants (10-20% aluminum chloride) | Obstructs sweat gland ducts | Moderate; first-line in mild-moderate cases | Requires continuous use (nightly) | None (topical) | Skin irritation, contact dermatitis |
| Iontophoresis | Low-voltage electrical current temporarily alters gland function | Moderate-high on palms/soles; less studied on underarms | 1-3 months; requires maintenance sessions (3-5 per week initially, then weekly) | None (non-invasive) | Erythema, vesicles, discomfort, skin cracks |
| Botulinum toxin (Botox/Dysport) | Blocks acetylcholine release at the neuroeffector junction of eccrine glands | High; 50-55% achieve ≥2-point improvement on HDSS | 4-12 months (average 7) | Minimal (intradermal injections) | Mild injection site pain, hematoma, compensatory sweating (<6%) |
| Oral anticholinergics (oxybutynin, glycopyrrolate) | Systemic blockade of muscarinic receptors | Moderate; ~60% report ≥1-point HDSS improvement | Effect only while taking medication (daily) | None (oral) | Dry mouth (43%), blurred vision (13%), constipation, urinary retention |
| miraDry (microwave) | Selective thermolysis of sweat and apocrine glands at the dermal-hypodermal interface | High; complete or near-complete resolution in many patients | Permanent or very prolonged (1-2 sessions) | Moderate (local anesthesia, external device) | Edema, pain, erythema; rare: inflammatory nodules, axillary alopecia, brachial plexus injury |
| Endoscopic thoracic sympathectomy (ETS) | Surgical section of the thoracic sympathetic chain | Very high (>90% for palmar sweating) | Permanent | High (thoracic surgery under general anesthesia) | Compensatory sweating (up to 70-98%), Horner syndrome, pneumothorax, bradycardia |
Botulinum toxin occupies an ideal middle ground: it offers high efficacy with minimal invasiveness and a favorable safety profile. Topical antiperspirants are usually the first step, and if insufficient, botulinum toxin is the recommended next line. Surgical or device-based options (miraDry, ETS) are reserved for refractory cases or patients seeking more permanent solutions, accepting a different risk profile.
Side effects and contraindications
The adverse effects of botox in underarms are generally mild, transitory, and localized.
Frequent adverse effects
- Injection site pain: mild, disappears within hours.
- Hematoma or ecchymosis: small bruises at injection points; resolve within days.
- Local itching or burning: transitory.
- Headache: uncommon, self-limited.
Compensatory sweating
Compensatory sweating—increased sweating in other body areas as a response to underarm blockade—is the most common patient concern. With botulinum toxin, the reported incidence is below 6% in controlled studies. This contrasts sharply with thoracic sympathectomy, where compensatory sweating is reported in 70% to 98% of patients. The difference is explained because botulinum toxin acts locally on sweat glands, whereas sympathectomy interrupts a central neural pathway that regulates sweating in multiple body areas.
When it occurs with botox, compensatory sweating is usually mild, transitory, and proportional to the duration of the treatment effect.
Contraindications
- Pregnancy and breastfeeding.
- Known allergy to botulinum toxin or any of its excipients.
- Active infection in the area to be treated.
- Neuromuscular diseases (myasthenia gravis, Lambert-Eaton syndrome).
- Concomitant use of aminoglycosides or other drugs that interfere with neuromuscular transmission.
Frequently asked questions
How does botox work in the underarms?
Botulinum toxin blocks the release of acetylcholine at the nerve endings that stimulate eccrine sweat glands, temporarily interrupting the signal that orders sweat production.
Unlike its cosmetic use where it relaxes muscles, in the underarms it is injected intradermally—in the skin layer where the glands reside—without affecting the underlying musculature. The effect is localized: only sweating in the treated area is reduced, while the rest of the body maintains its normal thermoregulatory capacity. You can learn more about the botulinum toxin mechanism here.
How long does the botox effect last in the underarms?
The effect lasts between 4 and 12 months, with an average of 6 to 7 months according to controlled clinical studies.
Variability depends on individual factors such as the severity of hyperhidrosis, the patient's metabolism, and the dosage used. In four-year longitudinal studies, the median duration per session ranged from 175 to 238 days. A relevant finding: at least 22% of patients maintained the benefit for a full year after the first session, and evidence suggests that repeated sessions can progressively extend the duration of effect.
How many units of botox are needed for the underarms?
The FDA-approved dosage is 50 units of Botox (onabotulinumtoxinA) per underarm, for a total of 100 units per session.
These 50 units are distributed across 10 to 15 injection points per underarm, spaced 1 to 2 cm apart, in aliquots of 0.1 to 0.2 mL. It is important to remember that Botox and Dysport units are not interchangeable: the approximate equivalence is 1 Botox unit for every 2.5 to 3 Dysport units. Your physician will determine the appropriate dosage according to the product used and the extent of the affected area, previously defined using the starch-iodine test.
Does botox in the underarms hurt?
Most patients describe the injections as mild discomfort, comparable to a small repeated pinch.
A 30-gauge needle is used, one of the finest available in medicine. Each underarm receives between 10 and 15 superficial injections (intradermal, only 2 mm deep), which reduces sensation compared to deeper injections. For patients with high sensitivity, a topical anesthetic (tetracaine cream) or ice can be applied 15-20 minutes before. The complete session lasts 15 to 20 minutes and does not require general anesthesia or sedation.
What is hyperhidrosis?
Hyperhidrosis is a condition characterized by the production of sweat that exceeds the physiological needs of thermoregulation, to the point of interfering with daily life.
It affects approximately 3% of the population. Primary hyperhidrosis—the most common—has no underlying medical cause, presents bilaterally and symmetrically, begins before age 25, and usually has a hereditary component. Secondary hyperhidrosis, on the other hand, is due to conditions such as thyroid disorders, diabetes, menopause, or certain medications, and requires addressing the cause first. The HDSS scale, from 1 to 4, allows severity classification: a score of 3 or 4 indicates severe impact.
Does botox in the underarms have side effects?
Side effects are generally mild and transitory: mild injection site pain, small bruises, and occasionally local itching.
The most frequently mentioned concern is compensatory sweating—increased sweating in other parts of the body—but with botulinum toxin the incidence is below 6% in clinical studies, significantly lower than with surgery (sympathectomy), where it can reach 70-98%. This is because toxin acts locally without interrupting central neural pathways. Contraindications include pregnancy, breastfeeding, neuromuscular diseases, and active infection in the area to be treated.
How often is botox applied in the underarms?
Most patients need one session every 6 to 9 months, although the interval varies from 4 to 12 months depending on individual response.
There is no fixed schedule: retreatment is performed when the patient notices that excessive sweating begins to return. The medical recommendation is to schedule the next session when the clinical effect of the previous injection noticeably diminishes. An encouraging finding is that with repeated sessions, many patients report progressively longer intervals between treatments, suggesting a cumulative effect on nerve endings.
Does botox in the underarms eliminate sweat completely?
No, and that is physiologically desirable. Botox drastically reduces excessive sweating—by up to 80% in patients with two-point improvement on the HDSS scale—but does not eliminate it completely.
The body retains some residual sweating capacity in the treated area, plus normal sweating in the rest of the body. The clinical goal is not total anhidrosis, but to bring sweat production to a functional and socially comfortable level. In clinical trials, 55-61% of patients achieved complete resolution (HDSS = 1, non-noticeable sweating), but even those who do not reach that level experience substantial improvement in quality of life.
What is compensatory sweating?
Compensatory sweating is increased sweating in untreated body areas (back, abdomen, legs, groin) in response to the blockade of sweating in the treated area.
With botulinum toxin in underarms, this phenomenon occurs in fewer than 6% of patients and is usually mild and transitory—it disappears when the treatment effect wears off. The situation is very different with endoscopic thoracic sympathectomy, where compensatory sweating is reported in 70% to 98% of cases, often in a permanent and even more debilitating way than the original hyperhidrosis. This radical difference is due to toxin acting locally, whereas surgery interrupts a nerve chain that influences sweating in multiple body areas.
Can botox be applied in the underarms in summer?
Yes, botox in underarms can be applied at any time of year, including summer.
There is no seasonal contraindication. In fact, many patients schedule their session in early spring or early summer to maximize coverage during the hottest months when sweating is greatest. The only post-treatment precautions are to avoid intense exercise and saunas for the first 24 hours. There is no need to avoid sun or apply special sunscreen in the area (the underarm rarely receives direct sun exposure). The time of year does not affect the efficacy or duration of treatment.
What is the difference between primary and secondary hyperhidrosis?
Primary hyperhidrosis is idiopathic (without known medical cause), bilateral, symmetric, with onset before age 25, and frequent hereditary component. Secondary hyperhidrosis has an identifiable underlying cause.
Causes of secondary hyperhidrosis include endocrine diseases (hyperthyroidism, diabetes, pheochromocytoma), menopause, infections, neurological diseases, and certain medications (SSRI antidepressants, opioids). Secondary can be unilateral, generalized, and accompanied by night sweats, features that primary typically does not present. This distinction is clinically crucial: secondary hyperhidrosis requires a complete medical evaluation to identify and treat the cause, not just the symptom. Botox and other local treatments are indicated for primary hyperhidrosis.
Does botox in the underarms affect body odor?
Yes, most patients report a noticeable reduction in axillary body odor after botox treatment.
Axillary malodor (bromhidrosis) occurs when bacteria on the skin surface decompose secretions from apocrine and eccrine glands. By drastically reducing sweating, the moist environment that favors bacterial proliferation is diminished, resulting in less odor. This effect is not the primary treatment indication—the goal is excessive sweating—but it is an additional frequently reported benefit that significantly improves patient quality of life and confidence in social situations.