Inflammation is generally defined as a biological response of the immune system in response to harmful stimuli. It is mainly associated with cardinal signs including pain, redness, tissue swelling, and heat (Begum et al., 2018). The process of inflammation is mediated via the chemical mediators secreting from inflammatory cells, typically injured tissue cells and migrating cells (Gunathilake et al., 2018). In addition, reactive oxygen species (ROS) enhance pro-inflammatory responses (Liu et al., 2022). Due to the instability of these radicals, they tend to stabilize through interaction with biological macromolecules such as protein, DNA, and lipids. Therefore, the accumulation of free radicals within the cells is another mechanism that leads to the induction of inflammatory disease conditions including cancer, diabetes, cardiovascular and neurodegenerative diseases (Rahman et al., 2015).

Non-steroidal anti-inflammatory drugs (NSAID) are mainly used to reduce pain and other inflammatory responses in disease conditions associated with inflammation. However, these are often associated with several adverse side effects such as epigastric pain and ulcers (Gunathilake et al., 2018). Therefore, many researchers have focused on finding natural sources as substitutes for these drugs recently.

Hibiscus rosa-sinensis belongs to the genus Hibiscus, which comprises about 275 species in tropical and subtropical regions and mainly thrives in warm climates around the world. Hibiscus rosa-sinensis is the most common hibiscus type in Sri Lanka and is widely known as the Shoe flower. H. rosa-sinensis is a member of the family Malvaceae and is grown as an evergreen herbaceous plant (Sarje et al., 2019). It is a versatile plant, with all parts having been used as traditional medications since ancient times (Begum et al., 2018). The plant possesses a large, single, or double layer, dark red color, and an ornamental flower that typically lacks fragrance. The flower H. rosa-sinensis is said to have many properties including antitumor, anti-inflammatory, anti-asthmatic, antipyretic, analgesic, antimicrobial, anti-fungal, and antioxidant (Mak et al., 2013, Guddeti et al., 2015, Goldberg et al., 2017, Missoum, 2018, Dwi Farasayu et al., 2021, Sanadheera et al., 2021, Sivaraman and Saju, 2021, Sruthi et al., 2021). According to many studies, most of these properties are attributed to polyphenolic and flavonoid compounds that act as secondary metabolites in many plants (Dahija et al., 2014, Liu et al., 2022). The phenolic and flavonoid composition of plant material is highly associated with environmental factors such as water availability, temperature, altitude, UV, soil, and humidity because these factors affect the metabolic activities and accumulation of secondary metabolites (Kabtni et al., 2020). Therefore, as a survival strategy, the phenolic and flavonoid composition varies with the climatic changes in different regions (Kabtni et al., 2020). Here, Figure 1 shows the two flowers of Hibiscus rosa-sinensis (red color single layer and double layer) which are the most commonly available in Sri Lanka.

Most of the research has been conducted to determine the anti-inflammatory potential of hibiscus leaves and roots, but there is less consideration given about its flowers. These studies are primarily based on in-vivo studies conducted with rats used as animal models. In-vitro studies related to the anti-inflammatory potential of H. rosa-sinensis flower extraction are rare to find. This flower widely used as a home remedy in Sri Lanka since ancient times, yet no detailed research has been performed, regarding the anti-inflammatory activity of hibiscus flower extraction in Sri Lanka. Therefore, the present review mainly focuses on the bioactive compounds present in Hibiscus rosa-sinensis flower extract and how these bioactive compounds contribute to inducing different mechanisms related to anti-inflammatory activity.