## 1 Introduction  
The skin, whose main role is to defend the body from external agents, presents also an important role that cannot be underestimated: feeling young and healthy, which helps in the social context [1]. However, this protection can be compromised with ageing due to reduced epidermal thickness and increased in wrinkles and dryness. Skin ageing is a complex biological process influenced by a combination of many factors related to intrinsic events as genetics, hormonal changes and metabolic processes, whereas ultraviolet (UV) radiation, pollution, or chemical exposure are more associated with environmental stressors (extrinsic events). All these factors lead to gradual but cumulative alterations where the formation of wrinkles, loss of elasticity, thinning of the skin, and roughness are some examples. Almost all of them are correlated with reduced extracellular matrix (ECM) proteins, especially collagen and elastin in the dermis [2, 3]. Collagen fibers represent the main component of ECM and they are responsible for the structural integrity and tensile strength of our body. Among 28 different types of collagens, types I and III are the most represented in the skin, with about 90% and 10% of the total. This proportion changes with age, highlighting a reduction approximately of 1.5% per year of the collagen produced together with an increase in its fragmentation. As shown by [PERSON] and colleagues, quantitative biochemical analysis showed that people with advanced age (80 years) had a quantity of fragmented collagen 4.3 times greater than in younger people aged between 21 and 30 years (in the human dermis) in vivo [4]. Elastin has the main function of providing elasticity to the tissues, being 10,000 times more flexible than collagen itself [5]. With ageing, the number of elastin fibers is also reduced. In addition to the physiological decay, chronic exposure to sunlight, in particular UV radiation, can cause a further worsening of the normal functions and characteristics of the skin. Among solar radiations, UVB are the most damaging rays, capable to induce DNA damage and the generation of excessive reactive oxygen species (ROS) production. ROS induce the activation of the mitogen-activated protein kinase (MAPK) cascade and the transcription factor named activator protein-1 (AP-1). The latter, in turn, regulates the transcription of metalloproteinases (MMPs), a large and complex family of zinc-dependent endopeptidases, able to break down almost all of the ECM components [6]. The MMPs can be classified according to their domains structure into collagenases, gelatinases, stromelysins, and matrilysins. Among all MMPs, the interstitial collagenase metalloproteinase-1 (MMP-1) is the most investigated. Its protease activity is addressed towards type I and III of collagens and it is produced by epidermal keratinocytes and dermal fibroblasts [7; 8; 9]. On the other side, many of these features are targets of the majority anti-ageing application or procedures for research strategies pertaining to the skin, from \"anti-wrinkle creams\" to various filling agents. It is noteworthy that the topical application of cosmetic products supplemented with functional compounds as antioxidant combinations or retinoids represents a valid way to contrast the signs of ageing. In this study, the effects of RETINOIDS SERUM (Matex Lab Spa, Brindisi, Italy) were taken under investigation for its innovative formulation enriched with vitamin A derivative characterized by a 1% of a retinoids mix including 0.1% of retinol, 0.1% retinaldehyde, and 1% of bioretinol. The retinoid class includes vitamin A (retinol), a 20-carbon molecule characterized by a cyclohexyl ring and an alcohol end group, and its synthetic and natural derivatives (retinaldehyde, retinoic acid, and retinyl esters). Retinoids are required in many cellular processes, such as cell growth and differentiation, apoptosis, inflammation, and immune modulation.