Current evidence suggests that rosacea occurs due to some combination of genetic predisposition and environmental influences. People with rosacea are four times as likely to have a relative with rosacea, and a genome-wide association study identified two gene variants strongly associated with rosacea.[1]
The symptoms of rosacea are thought to be caused by immune and neurovascular mechanisms that become dysregulated and overactive, leading to inflammation, redness, and blood vessel remodeling.[2] The factors driving this dysregulation are less clear and likely multifactorial.
Disruptions to the skin microbiome have been observed, and certain skin microbes have been identified as possible triggers for immune activation including Demodex mites, Bacillus oleronius, and Staphylococcus epidermidis.[2][3] A 2017 meta-analysis found that people with rosacea were over 800% more likely to be infested by Demodex mites, and had a greater density of these mites on their facial skin. However, a causal relationship could not be established due to study design.[4]