In today’s modern society, the importance of human interactions has increased, and in this setting appearance is a crucial factor in forming first impressions [1–3]. As social interest in maintaining a clean and healthy complexion rises, various methods for enhancing skin health have been developed across multiple fields. Skin disorders, particularly those affecting visible areas, are not only a cosmetic concern but can also lead to psychological distress, social withdrawal, and mental stress [4–6], ultimately lowering the quality of life [7,8]. Acne, a common skin disorder, exemplifies these issues [9].

Acne pathogenesis involves a complex interplay of factors, including increased sebum production due to androgens, hyperkeratinization of the follicular epithelium, proliferation of propionibacterium acnes (P. acnes) leading to inflammation, impaired skin barrier function, genetic predisposition, environmental influences, and follicular reactivity [10,11]. Androgens stimulate sebaceous glands to produce more sebum, which, combined with the thickened keratinocytes blocking pores, creates an environment conducive to P. acnes proliferation [12,13]. The bacterium breaks down triglycerides in sebum into free fatty acids, initiating an immune response that attracts white blood cells, causing inflammation and resulting in acne lesions [14,15].

Acne commonly begins during puberty, with males aged 15−19 and females aged 14−16 most frequently affected. Approximately 80 % of acne sufferers see their condition improve by their mid-20s [16,17]. However, adult acne can persist beyond adolescence into adulthood as persistent acne or can develop anew after age 25 as late-onset acne, with some women experiencing acne well into their 40s [18,19].

Effective acne management includes preventing the cohesion of desquamated keratinocytes, reducing or eliminating P. acnes, using comedolytics to clear clogged pores or anti-inflammatory agents to treat inflammatory responses, and reducing sebum production through decreased sebaceous gland activity [20,21].

Various treatment modalities have been developed for acne, including topical retinoids, hormonal therapy, topical antimicrobials, and oral antibiotics [22–25]. Recently, there has been increasing interest in cosmetic approaches to acne treatment [26], focusing on balancing oil and moisture levels and managing keratinization [27,28]. Concurrently, the demand for sustained and safe efficacy has grown, leading to the development of numerous anti-acne skincare products aimed at improving sebum production, keratinization, and pore condition [29]. Despite the proliferation of this market, scientific research on these products remains limited.

The non-thermal biocompatible plasma (NBP) electron density n_e = 1.6 × 10¹⁶ cm⁻³ and the molecular density in air is n_n = 3 × 10¹⁹ cm⁻³, and thus the ionization rate δ = n_e/n_n = 1/2,000. The NBP used in this study has the characteristics of a low-temperature plasma. In a typical plasma jet, the plasma used in this study has an electron density of 3 × 10¹⁴ to 3 × 10¹⁵ cm⁻³. In contrast, the NBP electron density is about 20 times higher. In other words, NBP, a direct plasma method, has more than 10 times greater bactericidal power than a plasma jet, an indirect plasma method [26].

The aim of this study is to evaluate the efficacy of a plasma device developed by B. C. Kim for the treatment of acne-prone skin [30–32]. In particular, this study is focused on the application of NBP, a novel technique that generates reactive species with broad biomedical applications, including acne treatment. NBP generated by air dielectric barrier discharge (DBD) plasma exhibits tissue-regenerative and sterilizing properties. The results indicate a significant increase in electron density correlating with peak current, highlighting the role of NBP in enhancing therapeutic outcomes for acne-prone skin.

2.1. Selection of test subjects

Subjects were selected from adult men and women over the age of 20 who had acne on their facial area. The principal investigator or a designated representative provided comprehensive information about the study to all potential participants. Subjects who agreed to participate did so voluntarily by signing an informed consent form. This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki, regulations of the Ministry of Food and Drug Safety concerning the designation of testing institutions for pharmaceuticals, quasi-drugs, cosmetics, and medical devices, the good clinical practice guidelines for pharmaceuticals, the guidelines for human application and efficacy testing of cosmetics, the guidelines for test methods for substantiating claims in cosmetic labeling and advertising, the guidelines for evaluating the efficacy of functional cosmetics, and the Bioethics and Safety Act of the Ministry of Health and Welfare. Additionally, the study followed the standard operating procedures of the Korea Institute of Dermatological Sciences. All procedures were monitored by a reliability assurance officer to ensure compliance and integrity.

For inclusion criteria for test subjects, the subjects had to meet the following: they were thoroughly informed by the principal investigator or a designated representative about the details of the study and voluntarily signed the consent form; healthy adult men and women over the age of 20 without acute or chronic physical conditions, including skin diseases; they were able to comply with follow-up visits throughout the study period; and subjects having facial acne, as confirmed by the principal investigator’s medical history and physical examination, with a global acne grading system (GAGS) score between 1 and 30 (Fig. 1).

Figure 1. Six points of the GAGS, which divides the face into six areas according to I to VI and assigns a factor for each lesion.

Exclusion criteria, on the other hand, were as follows: Subjects with known hypersensitivity to any components of the test products; subjects currently participating in another clinical study; pregnant or breastfeeding women; subjects who have used other acne treatments within the last month; subjects with severe systemic diseases or other dermatological conditions that could interfere with the study results; subjects who applied topical acne medications or steroids to their facial area within one month prior to the start of the study; subjects who underwent skin scaling, laser treatments, photodynamic therapy, or other skincare treatments for acne within one month prior to the start of the study; subjects with sensitivities or allergies to cosmetics or pharmaceuticals; subjects with severe acne, severe inflammation, eczema, psoriasis, skin cancer, or other serious skin conditions; subjects with skin conditions other than acne in the test area; subjects with atopic dermatitis; subjects deemed unsuitable for the study on the basis of the principal investigator’s judgment.

We also established dropout criteria for subjects, including cases where the study was terminated at the discretion of the principal investigator and cases excluded from the final analysis and report. These criteria included the occurrence of adverse events such as itching or erythema at the test site, the application of other topical agents, medication intake, injection therapy, or physical treatments such as laser therapy during the study that could interfere with the evaluation of the results, the application of medical treatment or other products, excessive ultraviolet exposure, excessive alcohol consumption, or smoking during the study that could affect the evaluation of results, the inability of subjects to continue follow-up due to personal reasons, and noncompliance with usage instructions or schedules without a valid reason.

2.2. Treatment dosage and administration of NBP

During the six-week study period, subjects applied NBP to the acneaffected areas on their faces five times for 2 s each time, twice daily, morning and evening, after cleansing their faces and removing any moisture. Following this, they evenly applied a cosmetic, Iodaze, to their entire face in the same amount, allowing it to absorb. During the human application study period, the use of any acne-improvement cosmetics other than the products provided by the research institute was strictly prohibited, and treatments such as facials or massages were also forbidden. Afterwards, subjects cleansed their faces with the same facial cleanser and rested for 30 min in a temperature and humiditycontrolled room (temperature: 22 ± 1 ∘C, humidity: 45 ± 5 %) before measurements were taken.

2.3. Assessment of suitability for NBP treatment of acne-prone skin

In this study, the suitability of the test product for use on acneprone skin was visually assessed by the principal investigator using the GAGS. The GAGS divides the face, chest, and back into six regions (forehead, right cheek, left cheek, nose, chin, chest, and upper back). Each region is evaluated for acne severity on a scale of 0−4 (0 = Nil, 1 = Comedone, 2 = Papule, 3 = Pustule, and 4 = Nodule). When multiple types of lesions are present in one region, the most severe lesion is scored. The scores from each region are then used to calculate the total GAGS score according to the following formula:

where the region factor is based on the surface area of each region. The total score classifies the acne severity of the subjects as follows: (i) 1-18 points: mild, (ii) 19-30 points: moderate, (iii) 31-38 points: severe, (iv) 39 points and above: very severe.

A decrease in the GAGS score compared to the baseline indicates suitability for use on acne-prone skin. Assessments were conducted at baseline (before product use), after two weeks of use, after three weeks of use, and after six weeks of use.

Evaluation of sebum improvement

In this study, the suitability of the test product for use on acneprone skin was evaluated using a DermaLab USB sebum probe (Cortex Technology, Inc., Denmark). Sebum measurements were conducted by the same investigator, who applied the sebum collector strip to the left nostril area of the test subject with consistent pressure for 30 s. Subsequently, the strip was inserted into a tape reader to calculate the degree of sebum absorption, represented as the percentage of film saturation (%). A decrease in the measurement values compared to those before application of the product indicates an improvement in sebum levels. Measurements were taken before application of the product and at two, three, and six weeks after initiation of product use.

Adverse reaction assessment

The study investigator observed the presence of skin reactions such as erythema, edema, scaling, itching, stinging, burning, tightness, or prickling on the test site. Any reactions were graded accordingly and documented.

2.4. Adverse events

Adverse event evaluations were conducted during each visit with the test subjects using the case report form. Skin reactions (erythema, edema, scaling, itching, stinging, burning, tightness, and prickling) or other abnormalities were assessed visually and recorded as mild, moderate, or severe. Instances of study discontinuation or withdrawal were noted in the case report form. Participants unable to continue the study on their scheduled visit days were required to sign a consent form for withdrawal from the study.

2.5. Statistical analysis

Statistical analysis of the study was performed using SPSS statistics 17.0 for Windows. Descriptive statistics including mean, standard deviation, frequency, and percentage were used to analyze the questionnaire responses. Paired t-tests were conducted to determine significant changes in various skin improvement measures based on device measurement results.

3.1. Evaluation of suitability for use on acne-prone Skin

Visual assessment for suitability by NBP treatment

For this experiment, we conducted the study with 21 participants, consisting of both males and females with a mean age of 27.19 years (SD = 6.46). The results of the visual assessment for suitability on acneprone skin using the test product, which was conducted by the study director with the GAGS before use and after two, three, and six weeks of use, are shown in Table I. The acne grading scores showed a reduction of 13.00 % after two weeks, 21.97 % after three weeks, and 26.91 % after six weeks of using the test product compared to before its use. Additionally, statistically significant differences were observed (p < .05) after two, three, and six weeks of use compared to before us, indicating that the test product is suitable for acne-prone skin (Fig. 2).

Figure 2. Full face photography by DermaLab USB sebum probe system. (a) 21-year-old male before using NBP; GAGS score change of 16 to 12 (after 6 weeks), (b) 27-year-old male before using NBP; GAGS score change of 9 to 4 (after 6 weeks).

Table I. Changes in acne grade score and improvement rate (%) after two, three, and six weeks of use (N=21). The results are presented as the mean ± standard deviation (SD) of three individual experiments. *p < 0.05, **p < 0.01, and ***p < 0.001..

	GAGS score
	Control	2 weeks	3 weeks	6 weeks
Average	10.62	9.24	8.29	7.76
SD	3.31	3.16	2.53	2.72
Improvement rate		13.00	21.97	26.91
p-value		0.030*	0.001**	0.000***

Evaluation of sebum improvement by NBP

The test was assessed using a DermaLab USB sebum probe after two, three, and six weeks (Table II). Analysis of sebum levels on the left nasal area using the DermaLab USB sebum probe showed a reduction in sebum production: 7.35 % after two weeks, 12.15 % after three weeks, and 25.11 % after six weeks compared to before using the test product. Moreover, statistically significant differences were observed after two, three, and six weeks of use (p < .01) compared to before use, indicating that the test product effectively improves sebum levels on acne-prone skin.

Table II. Changes in sebum level and sebum improvement rate (%) after two, three, and six weeks of use (N=21). The results are presented as the mean ± SD of three individual experiments. **p < 0.01 and ***p < 0.001..

	Control	Two weeks	Three weeks	Six weeks
Average	12.90	11.95	11.33	9.66
SD	6.25	6.25	6.19	6.02
Improvement rate		7.35	12.15	25.11
p-value		0.001**	0.000***	0.000***

3.2. Skin reactions due to NBP treatment

No allergic contact dermatitis or irritant contact dermatitis reactions were observed through the evaluation of skin reactions due to NBP treatment. We also conducted a skin reaction assessment based on participant surveys separate from the formal skin reaction assessment. No specific skin adverse events were reported in the participant surveys (Table III).

Table III. Adverse skin reactions reported by study participants after two, three, and six weeks of use (N=21)..

Adverse reaction	Two weeks	Three weeks	Six weeks
Erythema (redness)	0	0	0
Edema (swelling)	0	0	0
Scaling	0	0	0
Itching	0	0	0
Stinging	0	0	0
Burning sensation	0	0	0
Tightness, prickling	0	0	0

For this clinical study, a human application test was conducted on 21 adult male and female participants with acne-prone skin on the facial area using NBP, a zirconium surface DBD type plasma. According to the responsible investigator’s assessment using the GAGS and a DermaLab USB sebum probe, statistically significant improvements were observed compared to before product use. The acne grade score improvement rates were 13.00 % after two weeks, 21.97 % after three weeks, and 26.91 % after six weeks, all at a statistically significant level (p < .05). Additionally, statistically significant improvements in sebum reduction rates were 7.35 % after two weeks, 12.15 % after three weeks, and 25.11 % after six weeks (p < .01). Therefore, this zirconium surface DBD type plasma is considered suitable for acne-prone skin.

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2021R1A6A1A03038785) and by the Ministry of Science and ICT (MSIT, no 2022R1F1A1074105).

The authors declare no conflicts of interest.