Cosmetics are, per definition, any substance or mixture intended to be placed in contact with the external parts of the human body (epidermis, hair, nails, lips, and external genital organs) or with teeth or with the membranes of the oral cavity with the sole or main purpose to clean, perfume, change their appearance, protect, keep good condition, or alter body odors [9,10]. Cosmetic products with biologically active ingredients are formulated to improve appearance and boost positive physiological effects at the cellular level, and there is a high demand for these ingredients [2].

Skin is exposed to several external agents responsible for skin aging. Oxidative stress is mainly caused by reactive oxygen species (ROS) and is involved in many processes that damage the skin’s appearance by triggering cellular damage (Figure 1) [11,12]. Antioxidants consist of enzymatic (i.e., superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione transferase) and non-enzymatic (i.e., β-carotene, R-tocopherol, ascorbic acid, and ubiquinol) molecules with several activities, including photoprotection and scavenging/immobilizing of ROS, therefore preventing damage of the lipids, proteins, and DNA [2,13]. The oxidation of membrane lipids damages the appearance of the skin, and with aging, the body’s ability to regulate ROS increases, also increasing its mitochondrial production, culminating in skin aging. Thus, to halt this process, antioxidants can be incorporated into cosmetics to lessen oxidative stress [13].

The great majority of ROS (80%) are produced in response to solar radiation, with UV rays also reducing the activity of antioxidant enzymes [3,14]. Thus, solar exposure is the biggest contributor to skin aging through hyperpigmentation and photoaging (degradation of collagen and hyaluronic acid), causing wrinkles [1,15]. Hyperpigmentation refers to the overproduction of melanin in the skin and is considered an aesthetic problem [16]. The overproduction of melanin can be transitory or permanent and promoted by many factors including, as mentioned, UV radiation [7].

Skin whitening products focus on providing equal pigmentation of the skin by decreasing melanin’s concentration, and the market value for these products is growing and expected to reach 8.9 billion USD by 2027 [7,16]. Tyrosinase is the rate-limiting enzyme involved in the synthesis of melanin and is thus a good target for skin whitening products. The cosmetic industry is expanding the use of natural depigmentation ingredients, such as liquiritin, isoliquertin, aloesin, arbutin, and vitamin C, as these have fewer side effects than synthetic components and are eco-friendly [17,18].

Over the years, awareness of the skin damage caused by UV rays and solar exposure has increased and led to the production and commercialization of cosmetics with photoprotective properties [16]. Matrix metalloproteinases (MMPs) (i.e., collagenases, gelatinases, and stromelysins) are responsible for the degradation of proteins of the extracellular matrix (i.e., collagen, elastin, and hyaluronic acid) [19,20,21]. The expression of MMPs is stimulated by UV radiation, promoting skin aging through photoaging and the formation of wrinkles. Due their involvement in photoaging processes, compounds able to inhibit MMPs are of interest for the development of cosmetics to prevent photoaging of the skin and wrinkle formation [2,22]. In fact, anti-aging products are amongst the most marketed and commercialized cosmetics in the world [13,16]. The main process involved in the aging of the skin is the degradation of the extracellular matrix in the epidermal and dermal layers of the skin. Although genetics (intrinsic aging) are detrimental, extrinsic factors (i.e., exposure to UV radiation and pollution, nicotine, and lifestyle choices) also contribute to accelerating this process [2,3,23,24]. Most anti-aging cosmetics focus on stimulating the production of proteins of the extracellular matrix, such as collagen and glycosaminoglycan, to increase the firmness and elasticity of the skin [2,25,26].

Another very important aspect to increasing the firmness and elasticity of the skin is its hydration [27]. A disruption in skin hydration may lead to accelerated desquamation, and the usual cosmetic treatments for dehydrated skin include lipid-based moisturizers to retain water by occlusion. Collagen is a common constituent of moisturizers with well-known hydrating benefits [1,12,16]. Dehydrated skin is also characterized by a loss of hyaluronic acid, decreasing the skin’s elasticity. Thus, many cosmetics aiming to treat dehydrated skin contain hyaluronic acid; however, its role in skin rehydration is still controversial, as the higher the molecular weight of hyaluronic acid, the higher its moisturizing abilities [13,28,29,30]. In fact, the cosmetic applications of hyaluronic acid appear to change in relation to its molecular weight: high-molecular-weight hyaluronic acid rehydrates the skin by contributing to osmotic balance, and consequently stabilizes the extracellular matrix; hyaluronic acid of medium molecular weight enhances wound healing and cell repair by modulating inflammation and angiogenesis; while low-molecular-weight hyaluronic acid can be included in cosmetic formulations for both wound healing enhancement and moisturizing abilities [28,30].

Acne vulgaris is another skin disorder with significant prevalence. It is complex and multifactorial and usually associated with commensal skin microbiota, increased serum production, and hyperkeratosis [31,32,33]. Propionibacterium acnes and Staphylococcus epidermidis are the main bacteria involved, leading to the production of proinflammatory cytokines and the release of ROS, whose excessive production results in a destructive phenomenon, leading to scarring [2,34]. These bacteria also release lipases to digest the surplus of skin oil and sebum, which in turn stimulates an intense local inflammation that bursts from the hair follicles [35]. Therefore, the inhibition of both bacteria has been recognized as a strategic method for the management of acne in the cosmetics industry [2,32,35,36,37]. Acne vulgaris is conventionally treated with antibiotics, such as clindamycin and erythromycin, and in some cases, it entails oral antibiotics. Yet, extensive application of antibiotics might lead to bacterial resistance. Furthermore, antibiotics may cause skin allergies and irritation [31]. Owing to the multiple factors involved in the pathogenesis of acne and the implications of the use of antibiotics, it is important to highlight, for example, the bacterial growth-inhibiting activities of some marine ingredients [33,35].