The paper explains that a skin enzyme called kallikrein‑5 gets too active in rosacea, which then makes a protein called LL‑37 rise and cause redness, swelling, and extra blood vessels on the face. Treatments that calm down kallikrein‑5 or lower LL‑37 can improve these skin problems.

Rosacea is a chronic inflammatory condition of facial skin estimated to affect more than 16 million Americans. Although the pathogenesis of rosacea is not fully understood, recent evidence in vitro as well as in vivo has supported the role of increased levels of the trypsin-like serine protease, kallikrein 5, in initiating an augmented inflammatory response in rosacea. The increase in the quantity and magnitude of biological activity of kallikrein 5 leads to production of greater quantities of cathelicidin (LL-37), an antimicrobial peptide associated with increases in innate cutaneous inflammation, vasodilation, and vascular proliferation, all of which are characteristic features of rosacea. In this article, the authors review the literature supporting the role of kallikrein 5 in the pathophysiology of rosacea, including how therapeutic interventions modulate the effects of kallikrein 5, thus providing further support for this pathophysiological model that at least partially explains many of the clinical features of cutaneous rosacea.