Virtually nothing is known about causation. Possibilities which have been discussed include gastrointestinal disease, hypertension, Demodex folliculorum mites, emotional stress, etc. None of them has been proved. Rosacea patients are constitutionally predisposed to blushing and flushing. Sunlight and heat are definitely contributing factors. The influence of heredity is moot, as is almost everything that has been written about etiology.