Essential oils obtained from different parts of plants by distillation, extraction, and pressing techniques have many biological activities, such as antimicrobial, anti-inflammatory, antioxidant, anticarcinogenic, and wound healing. They are also secondary metabolites widely used in cosmetics, food preservation, drug delivery systems, and cleaning products. Aromatherapy, which is a preventive and complementary treatment system that includes the application of massage, mist, compress, bath, etc. for physiological and psychological well-being, is one of the techniques widely used all over the world. Essential oils and fixed oils are used in this method. It is important for human health that these oils are of pharmacopeia quality or International Organisation for Standardisation (ISO) standards. Today, adulteration of essential oils is one of the major problems in the world market. By adding lower-quality and cheaper synthetic or natural components to essential oils, human health is harmed, and unfair profits are made from these oils (Padovan et al., 2017).

Tea tree oil (TTO) is one of the most commonly used essential oils obtained by steam distillation from terminal branches or leaves of Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller, or other Melaleuca species. TTO has antibacterial, antiviral (e.g., Herpes simplex), insecticidal, antidermatophytic, analgesic, anti-inflammatory, antitumor, and acaricidal activities. It is also widely used in the treatment of acne and blepharitis. The European Medicines Agency recommends this oil for the symptomatic treatment of minor superficial wounds and insect bites, boils, and minor acne scars; the reduction of itching and irritation in mild cases of tinea pedis; and minor inflammations of the oral mucosa. In addition, the Cosmetic Ingredients database (Cosing) established by the European Commission on the ingredients of cosmetic products recommends its use in cosmetics as an antioxidant against oxygen-induced deterioration and as a perfume or aromatic raw material (European Commission, 2025). TTO is found in many different formulations, including in a variety of household products such as detergents and cleaners. This oil also has a wide range of uses in aromatherapy for infectious diseases such as skin diseases, respiratory system diseases, genitourinary diseases, colds, flu, and chicken pox. TTO, found in many pet shampoos, is used to kill ticks and fleas, as well as claimed to repel insects (Bejar, 2017, Padovan et al., 2017, Deliorman Orhan and Bulut, 2018). TTO is also formally recognised in various pharmacopoeial and regulatory standards, including the European Pharmacopoeia, due to its well-documented therapeutic properties. It is widely incorporated into cosmetic formulations and oral care products, particularly for its antimicrobial action in skin-related conditions such as acne. The increasing use of TTO in both therapeutic and cosmetic applications further highlights the importance of comprehensive quality assessment and standardisation (Sanyang et al., 2017, Sharifi et al., 2017, Kırcı et al., 2025).

In Türkiye, TTO, which is often used in aromatherapy for acne and dermatophyte infections, is supplied by pharmacies, aktars, and health food stores. In this study, TTO samples purchased from the market were analyzed for quality control according to the ‘Tea Tree Oil’ monograph in the European Pharmacopoeia 8.0, and the essential oil composition was elucidated by Gas Chromatography-Gas Chromatography/Mass Spectrometer (GC-GC/MS) method (European Pharmacopoeia, 2013). The essential oil samples were also tested for their antimicrobial activities against quality control strains (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pygones, Propionibacterium acnes, Lactobacillus plantarum, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Candida tropicalis, Candida parapsilosis, Microsporum gypseum, Trichophyton rubrum, Epidermophyton floccosum) for their antibacterial, antifungal and antidermatophytic activity.