## 1 Introduction  
Eyebrows are crucial to facial aesthetics and play a fundamental role in interpersonal communication. Research indicates that eyebrows may be as important as eyes in facial recognition. In contemporary beauty standards, thick and well-shaped eyebrows are considered key elements of attractiveness, particularly for women [1, 2, 3]. Hair loss negatively affects self-esteem, but eyebrow byprottosis receives less attention than scalp alopecia or eyelash hair loss [4, 5]. Conservative solutions to improve eyebrow appearance include traditional or permanent makeup, while eyebrow transplantation is an invasive option [6]. In this study, we focus on the impact of prostaglandin derivatives on eyebrow hair growth and thickening. Prostaglandins are naturally occurring eicosanoids derived from arachidonic acid. Known as paracrine hormones, they play a significant role in various physiological processes. Currently, 16 types of prostaglandlandins have been identified. Their local actions are diverse and often opposing, influencing processes such as inflammation, smooth muscle contraction, blood flow regulation, and chemotaxis [7]. Prostaglandin derivatives are synthetic analogs of naturally occurring prostaglandlandins. These compounds, known for their significant biological activity, have generated controversy regarding their use in cosmetics intended to promote hair growth [8]. According to the Scientific Committee on Consumer Safety (SCCS) report published in 2022, isopropyl clopstensate is considered safe when used at concentrations of 0.006% and 0.007%. In contrast, it is recommended that ethyl Raluprostamide should not be used at concentrations exceeding 0.018% [9]. However, the report included a caveat: the committee was unable to definitively determine safe concentrations of prostaglandin analogs in cosmetic products due to limited data. Attention was drawn to potential side effects from the uncontrolled use of these substances by consumers. Additionally, the report highlighted the regulatory discrepancies among EU member states regarding products containing prostaglandin analogs, complicating safety assessments. There is ongoing debate about whether prostaglandin analogs should be classified as cosmetics or medicinal products, given their significant biological effects [9]. Bimatoprost, a cosmetic ingredient, remains unassessed by the SCCS, although the Committee is ready to assess evidence supporting the safe use of prostaglandandins, including bimatoprost, in cosmetic products. On the other hand, market research suggests that the popularity of eyelash serums containing bimatoprost that are available both as prescription medicines and over-the-counter products is growing rapidly [10]. Bimatoprost is a prostaglandin analog used in cosmetic products to stimulate hair growth, including eyelashes and eyebrows [11; 12]. Bimatoprost amide, derived from dichloro-containing bicyclic ketone-6a, was initially developed as an ocular hypotensive agent [13]. Figure 1 shows the chemical structure of the precursor molecule of bimatoprost-dichloro-containing bicyclic ketone 6a (A) and the structure of the bimatoprost molecule (B) [13; 14]. Bimatoprost has proven highly effective in treating glaucoma and exhibits neuroprotective properties. This small, synthetic molecule, patented by Allergan, was found to stimulate eyelash growth as a side effect during glaucoma treatment, highlighting its potential application in cosmetics [11; 15]. Prostaglandin analogs were found to initiate hair regrowth and melanogenesis during the telogen stage and extend the duration of the anagen phase. Treated hair follicles exhibit larger-sized bulbs [16]. However, the mechanism by which bimatoprost stimulates hair growth is not fully elucidated. Prostaglandin analogs act through receptor-mediated stimulation of the PGF2-alpha receptor and activation of the canonical Wnt/\(\beta\)-catenin signaling pathway [17; 18].