The production of cathelicidin, an antimicrobial peptide is strongly increased in rosacea. Cathelicidin activates innate immunity, inflammation and angiogenesis. Cutaneous proteases produce inflammatory fragments of cathelicidin. UV-B irradiation and microbial components increase vitamin D3 and TLR2 expression in keratinocytes leading to an increase of cathelicidin production. Retinoids and doxycycline inhibit inflammation, proteases, angiogenesis and TLR2 expression. A multicenter study 2010 proved that isotretinoin with a dose of 0,3 mg/kg/d for 12 weeks and doxycycline with the dose of 100 mg/d for 14 days followed with 50 mg/d were equally effective. Doxycycline 40 mg/d is also effective in milder cases.