The study shows that the rosacea cream ivermectin not only kills parasites but also blocks a skin protein called LL‑37 and the enzyme KLK5 that creates it, cutting down inflammation in skin cells. This explains why the cream works for rosacea and suggests it can be used to manage the condition by targeting the immune pathway rather than just symptoms.

Numerous intrinsic and extrinsic factors have been associated with the pathophysiology of rosacea, including dysregulation of innate immunity. A high level of cathelicidin antimicrobial peptides (e.g., LL-37) has been shown in the facial skin of patients with rosacea. Excessive production of both LL-37 and KLK5, the serine protease responsible for its cleavage, has been suggested to play a role in the pathophysiology of rosacea. Ivermectin 10 mg/g cream, indicated for the treatment of inflammatory lesions of rosacea, is reported to have dual anti-parasitic and anti-inflammatory properties. However, the exact mechanism of action of ivermectin cream in the treatment of rosacea is unknown. This study aimed to evaluate the effect of ivermectin on the expression of KLK5 and the subsequent effect on the maturation process of cathelicidins. Experimental studies were performed either on normal human epidermal keratinocytes (NHEK), reconstructed human epidermis (RHE) or on human skin ex vivo stimulated with calcitriol (1α,25-dihydroxyvitamin D3), which is known to induce KLK5 and LL-37 expression. The results show that ivermectin is able to inhibit KLK5 and CAMP gene expression and protein secretion in NHEK cells stimulated with calcitriol. Those results were confirmed in 3D models of the skin (RHE and skin ex vivo). The anti-inflammatory effects of ivermectin were associated with an inhibition of IL-8, IL-6 and MCP-1 (CCL2) secretion from NHEK cells. These results suggest that ivermectin can prevent the inflammatory effects of rosacea triggered by abnormal LL-37 processing, through the inhibition of KLK5 gene expression in the epidermis. Nestlé Skin Health R&D.