Scientists tested citron essential oil on human skin cells in the lab and found it lowered several inflammation‑related proteins that are linked to rosacea, suggesting the oil could help calm rosacea symptoms, though the study was only done in cell cultures, not people.

Citron is well known for an abundance of antioxidative and anti-inflammatory ingredients such as vitamin C, polyphenol compounds, flavonoids, and limonoids. In this study, we aimed to evaluate the effects of citron essential oils on rosacea mediators in activated keratinocytes <i>in vitro</i>. Normal human epidermal keratinocytes (NHEKs) were stimulated with 1&#x3b1;, 25-dihydroxyvitamin D₃ (VD₃) and interleukin 33 (IL-33) with LL-37 to induce rosacea mediators such as kallikrein 5 (KLK5), cathelicidin, vascular endothelial growth factor (VEGF), and transient receptor potential vanilloid 1 (TRPV1). These mediators were analyzed by performing reverse-transcription polymerase chain reaction (PCR), quantitative real-time PCR, immunocytofluorescence and enzyme-linked immunosorbent assay after NHEKs were treated with citron seed and unripe citron essential oils. The messenger RNA (mRNA) and protein levels of KLK5 and LL-37 induced by VD₃ were suppressed by citron seed and unripe citron essential oils. Furthermore, the mRNA and protein levels of VEGF and TRPV1 induced by IL-33 with LL-37 were also suppressed by citron essential oils. These results show that citron essential oils have suppressive effects on rosacea mediators in activated epidermal keratinocytes, which indicates that the citron essential oils may be valuable adjuvant therapeutic agents for rosacea.