Acne vulgaris is a multifactorial disease which usually develops according to four main stages: sebum hyperproduction (seborrhoea), hyperkeratinization, colonization of Cutibacterium acnes (formerly Propionibacterium acnes), and resulting immune-mediated inflammation [2][5]. In turn, seborrhoea, being the upstream component, plays the key role in causing acne. Namely, hyperactivity of sebaceous glands leads to excessive secretion of sebum creating the lipid-rich environment for follicular clogging, bacteria reproduction, and inflammatory cascade activation. At the same time, seborrhoea itself causes other important aesthetic problems, namely increased oily facial skin, visible pores, uneven skin texture, skin shine, and decreased luminosity [5][6].

Seborrhoea is not a separate disease but rather a factor which increases the medical significance of acne and worsens its cosmetic impact. Despite the limited number of acne lesions, patients often experience discomfort related to the constant oiliness of their skin and prominent pores. For this reason, the treatment strategies should include sebaceous glands’ dysfunction as well as other components of the disease [4][7]. Standard first-line treatment of acne and seborrhoea includes topical retinoids, benzoyl peroxide, topical and oral antibiotics, hormonal modulators (combined oral contraceptives and spironolactone), and systemic isotretinoin. All these methods result in positive outcomes, although they do not provide full efficacy against seborrhea, are characterized by various side effects, cause local irritation, induce dry skin, promote development of antibiotic resistance, and exhibit high levels of recurrences when interrupted [3][8]. Notably, there exists a subgroup of patients that experience persistent oily skin despite optimally conducted therapy. Thus, there is a need for supplementary or alternative approaches that could modulate sebum production [7].

Recent developments suggest that intradermal administration of botulinum toxin type A can be used as an effective therapeutic approach for the treatment of seborrhoea and acne vulgaris. Known as an injectable cosmetic procedure aimed to paralyze muscles of the face, BoNT-A is supposed to lower sebum production through the inhibition of acetylcholine release at nerve terminals connected to sebaceous glands [2][5]. In this way, BoNT-A acts on a different pathway than antibacterial, comedolytic, or anti-inflammatory mechanisms involved in the development of acne and seborrhoea. Namely, the injection technique that uses micro-droplets does not affect muscle tissue [9][10].

Clinical observations and further studies proved the beneficial effect of BoNT-A administration on patients with acne vulgaris and seborrhoea. First, initial reports showed improvements in terms of facial oiliness, decreased pores, and improved skin texture [8]. More reliable information came from randomized and split-face controlled trials where a decrease in the production of sebum was observed, along with a reduction in the number of acne lesions and improved skin condition [10]-[12]. Reviews of off-label uses of BoNT-A suggested the possibility of improvement of skin quality factors, including reduction of sebum secretion and increase in luminosity due to microtoxin technique implementation [4][6][13].

However, despite such promising results, there are some limitations in the existing literature. Studies are characterized by the small sample size, relatively short period of follow-up (mostly up to 4 - 12 weeks), heterogeneity of injection technique (diffuse or varying amounts of micro-droplets of the drug), absence of a standard measure of efficacy (sebum level measured with sebumetry devices), and lack of long-term follow-up [7][10]. In addition, there are issues associated with the inability of BoNT-A to completely eliminate bacterial infection and inflammation and the possible side effects related to the use of this method (e.g. temporary ptosis or asymmetry in expressive areas of the face) [14]-[16]. Since this is an off-label indication, more prospective evidence needs to be collected to integrate it into practice.

Thus, there is a lack of information concerning the real efficiency and safety of BoNT-A injections for the treatment of seborrhoea and acne vulgaris. It is needed to carry out prospective interventional studies where the standard protocol will be followed (consisting of a particular micro-droplet intradermal technique), objective and subjective criteria will be used for the assessment of outcome (including sebumetry and lesion count, as well as validated scales for patients), sufficient follow-up period will be provided within the pharmacodynamic period, and safety analysis will be conducted. Such a study will give an opportunity to obtain clinically valuable information about the effectiveness of BoNT-A microinjections as the adjunctive procedure.

In order to fill the gap identified above, the current prospective study was designed to evaluate the efficacy and safety of standardized intradermal BoNT-A injections in patients with mild-to-moderate acne vulgaris and seborrhoea. Primary data will be provided concerning objective and subjective changes, including reduced sebum content and acne lesion number and patients’ satisfaction, duration of treatment efficacy, and adverse events.

The aim of this prospective single-centre interventional study is to examine the efficacy and safety of standardized intradermal botulinum toxin type A microinjections for sebum reduction and improvement of acne vulgaris in adults with concurrent facial seborrhoea.

To estimate objective sebum reduction through sebumetry measurements in pre-post protocol.

To measure changes in inflammatory and non-inflammatory acne lesion counts based on standard assessment and photographs.

To measure patient-reported outcomes using Visual Analogue Scale (VAS) and global aesthetic improvement score.

To record the safety profile and adverse events.

To investigate the duration of BoNT-A effects and its potential role as an adjunctive modality in aesthetic dermatology practice.

A prospective, single-centre, single-arm, open-label design using a within-subjects comparison method was employed. This design was chosen to provide clinically relevant results on the effectiveness of the tested procedure while ensuring that each participant served as his or her own control. The single-arm design was justified for this interventional experiment because it minimised the risk of confounding factors and allowed in-depth analysis of temporal changes in participants’ status. The study involved one screening visit, one treatment visit at week 0, and three follow-up visits at weeks 4 (peak of effect), 8, and 12.

The study was conducted at a specialised aesthetic dermatology clinic in the United Kingdom between March 2025 and December 2025. This setting provided access to standardised photographic equipment in a controlled clinical environment as well as calibrated measuring devices.

Participants were recruited via advertisements posted in the clinic and through patient referrals. Based on effect sizes estimated from previous studies, a minimum required sample size of 42 participants was calculated to achieve 80% power for detecting a 30% reduction in sebum production with α = 0.05, while accounting for possible attrition rates of up to 15%.

Strict eligibility criteria were applied to ensure participant safety, population homogeneity, and applicability of findings to the target aesthetic dermatology population (Table 1).

Table 1. Inclusion and exclusion criteria.

All participants underwent comprehensive medical screening, including detailed dermatological examination, medical history review, and assessment of contraindications to BoNT-A.

BoNT-A (onabotulinumtoxin A) was reconstituted according to manufacturer guidelines at a concentration of 4 units/0.1 mL (100 units diluted in 2.5 mL preservative-free sterile saline). Each microdroplet injection delivered approximately 0.05 - 0.1 mL (2 - 4 units) using a 30 - 32 G needle. The total dose for each participant (within the 40 - 60 units range) was selected according to facial surface area and baseline sebum distribution: participants with smaller facial surface area or milder seborrhoea received 40 - 45 units; those with larger facial surface area or higher baseline sebum received 50 - 60 units. Dose selection was performed by the treating clinician at the treatment visit using a pre-defined anatomical grid. Injections were performed by a board-certified aesthetic practitioner with extensive experience in neuromodulator techniques under direct supervision.

A total dose of 40 to 60 units per participant was distributed across the forehead, cheeks, and chin using a uniform micro-droplet grid pattern of 2 - 4 units per 2 cm². Superficial intradermal injections were administered at a 30˚ - 45˚ angle using 30 - 32 G needles to minimise diffusion to underlying musculature. Precise anatomical mapping was performed to avoid high-risk zones associated with complications such as ptosis or asymmetry (Table 2).

Table 2. Injection protocol summary.

No routine topical anaesthesia was required, although ice packs were offered for patient comfort. Post-treatment instructions included avoidance of strenuous exercise, heat exposure, facial massage, and alcohol consumption for 24 hours (Figure 1).

The primary outcome was change in facial sebum secretion, objectively measured using the calibrated Sebumeter SM 815 (Courage + Khazaka, Germany) in arbitrary units (AU) on three specified areas (forehead, right cheek, and left cheek). Prior to each visit, participants were instructed to avoid all topical skin products (including moisturisers, sunscreens and make-up) for at least 4 hours and to refrain from washing the face for at least 2 hours. Upon arrival, participants acclimatised for 20 minutes in a controlled environment (room temperature 20˚C - 22˚C, relative humidity 40% - 60%). Three consecutive readings were obtained at each of the three sites; the mean of the three readings per site was calculated, and the overall facial sebum value was defined as the arithmetic mean of the three site means. The primary prespecified comparison was the paired change from baseline to week 4 (the anticipated peak-effect time point).

Secondary outcomes included counting of inflammatory lesions (papules and pustules) and non-inflammatory lesions (open and closed comedones), performed manually under standard conditions and assisted by high-definition photographs. Patient-reported outcomes were assessed using a 10-point Visual Analogue Scale (VAS) for satisfaction and the Global Aesthetic Improvement Scale (GAIS). Clinician-based evaluation of skin appearance was performed through

BoNT-A: Botulinum toxin type A.

Figure 1. Study flow diagram.

assessment of photographs, blinded when possible.

Safety outcomes were actively queried and recorded, with specific attention to injection-related reactions, ptosis, asymmetry, bruising, erythema, and systemic manifestations.

Baseline measurements were obtained before treatment initiation at week 0. Follow-up examinations were conducted at weeks 4, 8, and 12. Data were collected using standardised electronic case report forms with automated validation and double data entry.

All data were statistically analysed using SPSS version 28.0 (IBM Corp., Armonk, NY). Summary measures (mean, standard deviation, frequencies, and percentages) characterised baseline parameters and endpoints. Changes from baseline were assessed using paired Student’s t-test for normally distributed data and the paired Wilcoxon signed-rank test for non-parametric distributions. The primary analysis was the paired mean change in overall facial sebum (AU) from baseline to week 4, with a two-sided 95% confidence interval. Repeated-measures analysis of variance (or the Friedman test in cases of non-normal distribution) was employed to evaluate the effect of time on repeated measurements, followed by post-hoc Bonferroni correction. Possible effect modifiers (age, gender, baseline sebum content, and severity of acne) were examined through subgroup analysis. Statistical significance was defined as p < 0.05 (two-tailed).

The study was reviewed and approved by the ValMari Aesthetic Education Center Institutional Review Board (approval identifier: VMEC-IRB-2025-003, dated 12 February 2025). The study was conducted in accordance with the ethical principles of the Declaration of Helsinki (2013 revision) and applicable ethical standards for research involving human participants. All participants provided written informed consent before participation and were informed about the study procedures, the off-label use of botulinum toxin type A, potential risks and benefits, and their right to withdraw from the study at any time. Participant confidentiality and anonymity were maintained throughout the study, and study data were handled in accordance with applicable data-protection requirements.

A rapid, statistically significant, and clinically meaningful reduction in facial sebum production was observed following intradermal BoNT-A microinjections, with effects sustained throughout the 12-week follow-up period. Mean sebum levels, objectively measured using the Sebumeter SM 815, decreased from a baseline

Table 3. Baseline demographic and clinical characteristics of study participants (n = 42).

value of 142 ± 28 AU to 74 ± 19 AU at week 4, corresponding to a 47.9% reduction (mean paired change −68 AU, 95% CI −78 to −58; p < 0.001). Although a gradual partial rebound was noted thereafter, clinically relevant suppression persisted at later time points, with reductions of 40.8% at week 8 (84 ± 22 AU, p < 0.001) and 35.2% at week 12 (92 ± 25 AU, p < 0.01). Repeated-measures ANOVA demonstrated a highly significant effect of time (F = 68.4, p < 0.001), and post-hoc Bonferroni-adjusted analyses confirmed that all follow-up measurements differed significantly from baseline.

Regional analysis indicated consistent sebosuppressive effects across all measured facial zones (forehead, right cheek, left cheek), with the most pronounced reduction observed in the cheeks (52% at week 4), followed by the forehead (46%). Chin sebum was also assessed clinically as part of the injection protocol but was not included in the primary Sebumeter composite; exploratory chin readings showed an approximate 38% reduction at week 4, consistent with the overall pattern. This pattern suggests a robust response of sebaceous gland-rich areas to the standardized micro-droplet injection protocol (Figure 2).

Treatment with intradermal BoNT-A was also associated with marked improvements in both inflammatory and non-inflammatory acne lesions. Inflammatory lesion counts (papules and pustules) decreased from a baseline mean of 18.4 ± 7.2 to 13.2 ± 6.1 at week 4 (−28.3%, p < 0.05), reaching a maximal reduction of 41.8% at week 8 (10.7 ± 5.1, p < 0.01). At week 12, inflammatory lesions remained

AU = Arbitrary Units (Sebumeter SM 815). Values are mean + standard deviation. *p < 0.001 vs. baseline; †p < 0.01 vs. baseline (Bonferroni-corrected post-hoc analysis).

Figure 2. Mean facial sebum production over time following intradermal BoNT-A Microinjections.

significantly reduced at 37.5% below baseline (11.5 ± 5.4, p < 0.01), indicating sustained clinical benefit.

Non-inflammatory lesions (open and closed comedones) showed a slower but consistent improvement, with reductions of 19.5% at week 4 (19.8 ± 8.4), 31.3% at week 8 (16.9 ± 7.8, p < 0.05), and 28.0% at week 12 (17.7 ± 8.2) (Table 4).

Table 4. Changes in acne lesion counts from baseline.

Satisfaction with the treatment remained high throughout the study period. Mean VAS scores increased to 7.8 ± 1.4 at week 4, reached a maximum of 8.2 ± 1.2 at week 8, and remained elevated at 7.5 ± 1.6 at week 12. On the GAIS, 81% (n = 34) of participants reported their skin as “much improved” or “very much improved” at week 8, with 69% (n = 29) still reporting this level of improvement at week 12. Patient feedback commonly described reduced facial shine, smaller-looking pores, smoother skin texture, and an overall healthier appearance finding that were consistent with the objective improvements in sebum levels and acne lesion counts (Figure 3).

*p < 0.001 vs. baseline (paired t-test with Bonferroni correction). GAIS categories: Very Much Improved/Much Improved/Slightly Improved/No Change/Slightly Worse/Worse.

Figure 3. Patient satisfaction (VAS) and global aesthetic improvement (GAIS) over time.

The procedure demonstrated an excellent safety and tolerability profile. No serious adverse events occurred during the study. All reported side effects were mild, transient, and resolved spontaneously without treatment. Mild injection-site erythema occurred in 11.9% (n = 5) of participants, minor bruising in 7.1% (n = 3), and temporary forehead tightness in 2.4% (n = 1). All events resolved spontaneously within 3 - 7 days. No cases of ptosis, facial asymmetry, muscle weakness, or systemic complications were observed (0%, n = 0) (Table 5).

Table 5. Summary of adverse events.

Exploratory subgroup analyses indicated a trend toward greater sebum reduction in participants with higher baseline sebum output (>150 AU) and in female participants compared with males; however, these differences did not achieve statistical significance within the current sample size. Improvements were broadly consistent across Fitzpatrick skin phototypes, age categories, and baseline acne severity (IGA 2 versus IGA 3), suggesting that improvements were observed across the subgroups represented in this study.

Overall, the findings demonstrate that a single session of standardised intradermal BoNT-A microinjections was associated with rapid, marked, and sustained reductions in sebum production and acne lesion counts. These objective improvements were accompanied by high levels of patient satisfaction and a favourable safety profile, with minimal and transient adverse effects in adults presenting with mild-to-moderate acne and facial seborrhoea.

This study’s strengths include its prospective design, objective primary outcome (Sebumeter measurements), standardised injection protocol, comprehensive assessment combining clinical, instrumental, and patient-reported outcomes, and complete 100% (n = 42) follow-up over 12 weeks. However, the absence of a concurrent control group limits causal inference; observed reductions are therefore described as occurring after treatment rather than as established treatment effects. The modest sample size (n = 42) and relatively short follow-up restrict conclusions regarding long-term durability, optimal retreatment intervals, and cumulative effects. In addition, the single-centre cohort may limit generalisability to broader populations, including different ethnic groups and more severe acne phenotypes.

These findings support intradermal BoNT-A as a useful adjunctive option for patients seeking rapid improvement in seborrhoea, acne lesions, and overall skin quality, particularly when conventional treatments are insufficient or poorly tolerated. However, it should be viewed as part of a multimodal approach rather than a standalone therapy, given its limited effect on microbial colonisation and deeper inflammatory pathways.

Further large-scale, multicentre, double-blind randomised controlled trials are needed to confirm these findings, optimise dosing and retreatment schedules, and evaluate long-term efficacy and cost-effectiveness. Comparative studies against standard acne therapies, as well as combination protocols and mechanistic investigations using imaging or histology, would further clarify its role in sebaceous gland modulation. Broader population studies across diverse skin types and hormonal acne subgroups are also warranted.

In conclusion, this study provides prospective evidence that standardised intradermal BoNT-A microinjections are associated with safe, effective, and well-tolerated reductions in sebum production and improvements in acne outcomes in adults with mild-to-moderate disease. The findings meaningfully expand the evidence base for neuromodulatory approaches in aesthetic dermatology and support further rigorous investigation to define their optimal clinical role.