**1. Introduction**

Seaweeds have received lot of attention in recent years because of their incredible potential. Seaweeds are essential nutritional sources and traditional medicine components [1]. Marine macroalgae, sometimes known as seaweeds, are microscopic, multicellular, photosynthetic eukaryotic creatures. Based on their coloration and depending on their taxonomic classification, they can be classified into three groups: Rhodophyta (red), Phaeophyceae (brown), and Chlorophyta (green). The global variety of all algae (micro and macro) is estimated to consist of over 164,000 species with roughly 9800 of them being seaweeds,

**Citation:** El-Beltagi, H.S.; Mohamed, A.A.; Mohamed, H.I.; Ramadan, K.M.A.; Barqawi, A.A.; Mansour, A.T. Phytochemical and Potential Properties of Seaweeds and Their Recent Applications: A Review. *Mar. Drugs* **2022**, *20*, 342. https://doi.org/ 10.3390/md20060342

Academic Editors: Donatella Degl'Innocenti and Marzia Vasarri

Received: 11 April 2022 Accepted: 21 May 2022 Published: 24 May 2022

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just 0.17% of which have been domesticated for commercial exploitation [2]. In recent years, seaweed has gained in popularity, making it a more versatile food item that may be used directly or indirectly in preparation of dishes or beverages [3]. Many types of seaweed are edible, they provide the body with a different variety of vitamins and critical minerals (including iodine) when consumed as food, and some are also high in protein and polysaccharides [4].

Seaweeds are now used in several industrial products as raw materials such as agar, algin, and carrageenan, but they are still widely consumed as food in several nations [5]. Seaweeds are frequently subjected to harsh environmental conditions with no visible damage; as a result, the seaweed generates a wide variety of metabolites (xanthophylls, tocopherols, and polysaccharides) to defend itself from biotic and abiotic factors such as herbivory or mechanical aggression at sea [6]. Please note that the content and diversity of seaweed metabolites are influenced by abiotic and biotic factors such as species, life stage, nutrient enrichment, reproductive status, light intensity exposure, salinity, phylogenetic diversity, herbivory intensity, and time of collection; thus, fully exploiting algal diversity and complexity necessitates knowledge of environmental impacts as well as a thorough understanding of biological and biochemical variability [7,8].

Seaweeds and their products are particularly low in calories but high in vitamins A, B, B2, and C, minerals, and chelated micro-minerals (selenium, chromium, nickel, and arsenic), as well as polyunsaturated fatty acids, bioactive metabolites, and amino acids [9]. Although current research revealed that the amount of specific secondary metabolites dictates the effective bioactive potential of seaweeds, phenolic molecules are prevalent among these secondary metabolites [10]. Furthermore, integrating seaweed into one's daily diet has been linked to a lower risk of a range of disorders, including digestive health and chronic diseases such as diabetes, cancer, or cardiovascular disease, according to research mentioned by [11]. As a result, incorporating seaweed components into the production of novel natural drugs is one of the goals of marine pharmaceuticals, a new discipline of pharmacology that has evolved in recent decades.

The \$4.7 billion worldwide algae products market is predicted to increase at a compound yearly growth rate of 6.3% to \$6.4 billion by 2026. North America has the highest proportion of the algae market [6]. Functional and nutritional attributes, as well as the potential sustainability benefits of algae, are driving demand and positioning it as a promising food of the future. The potential uses of different algae are numerous: generation of energy [12], the biodegradation of urban, industrial and agricultural wastewaters [13,14], the production of biofuels [15], the exclusion of carbon dioxide from gaseous emissions via algae biofixation [16], the manufacturing of ethanol or methane, animal feeds [17], raw material for thermal treatment [18], organic fertilizer or biofertilizer in farming [17]. The high protein content and health advantages have fueled an interest in foods derived from entire algae biomass [19]. Algae can be used as functional ingredients to boost food's nutritional value [20]. In cosmeceuticals, marine algae have received a lot of interest [21]. Seaweeds are one of the most abundant and harmless marine resources, with little cytotoxicity effects on people. Marine algae are high in bioactive compounds, which have been demonstrated to have significant skin advantages, especially in the treatment of rashes, pigmentation, aging, and cancer [22]. The use of algal bioactive components in cosmeceuticals is growing quickly since they contain natural extracts that are deemed harmless, resulting in fewer adverse effects on humans. Marine algae were used as a medicine in ancient times to treat skin problems such as atopic dermatitis and matrix metalloproteinase (MMP)-related sickness [22]. In summary, marine algae represent a promising resource for cosmeceutical production.

This review aimed to study the bioactive compounds in seaweeds and the role of these compounds as antioxidants, anti-inflammatory, anti-cancer, antimicrobial and anti-diabetic activities.
