## 3 Discussion  
Studies are scarce evaluating the effectiveness of micro-needle and needle-free mesotherapy treatments on the skin, including histological analyses, examining the effects of the therapy and snail-mucus-containing preparations on the skin. The literature review also lacks data on the duration of the effects of a series of mesotherapy treatments. The first stage of the study was to evaluate the morphology of skin with photoaging features by light microscopy before and after a series of mesotherapy treatments, including morphometric analysis. Important parameters indicative of the regeneration of skin overexposed to UV radiation include epidermal thickness and the thickness of collagen fiber bundles. In skin with photoaging features, thickening of the epidermis can be observed. It is associated, among other things, with the hypertrophy of sebaceous glands, an increase in their secretory activity, excessive keratinization of the epidermis, and an increase in the number of inflammatory cells, caused by chronic exposure to UV radiation. In addition, the thickening of the different layers of the epidermis is a consequence of UVB radiation, which affects the increased proliferation  
Figure 7: Immunoexpression of PCNA in skin of patients before and after 3 months of treatment. (**A**,**B**) Micro-needle mesotherapy + snail mucus 98.2%; (**C**,**D**) micro-needle mesotherapy + NaCl; (**E**,**F**) needle-free mesotherapy + snail mucus 98.2%. Obj. magn. 40\(\times\). Scale bar: 100 μm. of keratinocytes with a decrease in the number of Langerhans cells. Increased numbers of mast cells, fibroblasts, and macrophages are also observed [32; 33]. Morphometric analysis of patients' skin before treatments and 3 months after therapy showed a statistically significant reduction in epidermal thickness in each analyzed group A, B, and C. Similar results were obtained by [PERSON] et al. (2009) [34]. Our results suggest that micro-needle mesotherapy improves skin condition when considering the morphometry of the epidermis. In the present study, statistically significant differences were observed in the thickness of collagen fiber bundles in the reticular layer of the skin, which increased by 43% after a series of micro-needle mesotherapy treatments with snail mucus, by 33.8% after a series of micro-needle mesotherapy treatments with NaCl solution, and, importantly, by 17% after a series of needle-free mesotherapy treatments with snail mucus. The analysis of skin biopsy specimens showed positive changes in the morphology of collagen fibers, both types I and III, and elastic fibers in patients who were treated with snail-mucus-containing products applied by both micro-needle and needle-free mesotherapy. However, the greatest accumulation of elastic fibers in the dermis was observed in patients who received a series of needle-free mesotherapy treatments with snail mucus. It suggests that snail filtrate may have a beneficial effect on the condition of the skin. Changes in the skin after therapy with the use of snail mucus can be associated with the presence of allantoin in its composition, which has beneficial effects, among other things, on intercellular cement density and hydration, which is important in skincare, including in patients with features of photoaging. In addition, its use in daily care accelerates wound healing by stimulating fibroblast proliferation and the production of extracellular matrix components [16; 18; 35]. The above results may be also observed with skin micro-needle alone, which stimulates the synthesis of ECM components, including type I collagen, type III collagen, and elastic fibers, as demonstrated by the results of the present study and studies by other authors [31]. A similar study analyzing the effect of snail mucus filtrate on wound healing was conducted by [PERSON] et al. (2021) [36] in mice, which undoubtedly does not fully correspond with effects on human tissues.