Rosacea is a common and chronic skin disease characterized by facial flushing, papules and/or pustules, and visible blood vessels. The cause of rosacea remains poorly understood, although genetic and environmental factors likely contribute. Twin research has been instrumental during the past 20 years in demonstrating the heritability of disease such as psoriasis, eczema, and acne. In this cohort survey of identical and fraternal twins, Aldrich et al found that approximately half of rosacea symptoms could be attributed to genetics and half to the environment. Correlations between rosacea and UV radiation, alcohol use, smoking, skin cancer history, cardiac morbidity, and age were identified.