## 1 Introduction  
Defined as dispersions between oil, surfactant, aqueous phase, and, frequently, co-surfactants, microemulsified systems were discovered in 1943 by [PERSON] and [PERSON], who observed that an opaque emulsion stabilized by a surfactant became clear after the addition of a medium-chain length alcohol [1, 2]. By changing the proportions of components, it is possible to prepare different microstructures that can be classified into three categories according to their physicochemical properties, namely oil-in-water, bicontinuous, and water-in-oil microemulsions [3]. Several advantages are provided by microemulsionsover conventional formulations including ease of manufacturing, improved drug solubilization, good thermodynamic stability, protection against enzymatic hydrolysis, greater hydrophilic, hydrophobic and amphiphilic drug permeation, enhanced absorption due to surfactant-induced permeability, and increased bioavailability of hydrophobic compounds [4; 5]. Consequently, microemulsions have been extensively studied as a promising system for the delivery of hydrophilic, lipophilic, or amphiphilic bioactive compounds in pharmaceutical, nutraceutical, and cosmetic applications [6]. Chrysin (5,7-dihydroxy flavone) consists of a natural flavonoid, found in honey, propolis [7], and in species of many plants such as _Oroxylum indicum_[8] and passion flower (_Passiflora caerulea_ and _Passiflora incarnata_) [9; 10]. It is regarded as \"Generally Recognized as Safe\" (GRAS) by the U.S. Food and Drug Administration (FDA) and commonly used in the U.S. market as a nutraceutical [11] and food supplement without side effects [12] as well as being one of the flavonoids responsible for the biological and functional properties of honey, royal jelly [13], and propolis [13; 14]. Like other flavonoids, chrysin exhibits a broad-spectrum of pharmacological activities including as an antioxidant [8], antihemolytic [15], antitumor [16], hypolipidemic [7] and anti-hypertensive [17]. It is also reported to exert antinociceptive [18] and anti-inflammatory effects being able to inhibit several cytokines, nitric oxide, prostaglandin E, and cyclooxygenase-2 [10]. Additionally, it is an aromatase (estrogen synthetase) inhibitor used as a dietary supplement [19; 20]. Due to its abundance in plants, potential pharmacological and nutritional effects along with low systemic toxicity, chrysin is attracting considerable interest as an alternative to conventional therapeutic drugs. However, the use of chrysin as a drug is often hindered by its low water solubility (0.005 mg/mL), which greatly limits its bioavailability [11; 21; 22]. Hence, encapsulation within suitable delivery vehicles has been suggested as a method to overcome this drawback. Inflammation is the response to tissue injury caused by endogenous and/or exogenous stimuli. It is characterized by biochemical, vascular, and cellular changes that lead to the activation of cellular and plasma components of the immune system, in order to remove the offending agent and restore tissue homeostasis [23]. Hyperalgesia is one of the main causes of the inflammatory process that occurs through the activation of cytokine cascade, resulting in the sensitization of nociceptive primary sensory neurons [24; 25; 26]. The drug therapies currently available to treat inflammatory diseases act through various mechanisms; however, if used for a long time, they are responsible for significant side effects. Therefore, other therapeutic options are being explored in the treatment of inflammatory pain [23; 27]. In this context, as pro-inflammatory responses and the regulation of nociceptive sensitivity share common pathways, the property of flavonoids to inhibit pro-inflammatory stimuli may be successfully exploited to treat several acute and chronic inflammatory diseases as well as nociceptive sensitivity [18].