Aetiology & Pathogenesis
The cause of rosacea remains unknown. However, the most likely starting point is the presence of bacteria and Demodex mites in the skin. Lastly, the case of heredity is being considered and many studies are underway.
The microscopic Demodex mites are part of the ecologic community of microorganisms living inside and on the surface of the human body. Two types of Demodex mites have been identified in humans:
- Demodex folliculorum:which live in the hair follicles mainly on the face, as well as on the Meibomian glands of the eyelid. While Demodex folliculorum are found on the skin of almost everyone, often those who have rosacea have greater numbers of mites.
- Demodexbrevis: live in the sebaceous glands of the skin.
Research evidence suggests that the excessive number of Demodex can possibly cause an immune response in people with rosacea, or that inflammation can be caused by certain bacteria (Bacillus oleronius) associated with Demodex mites.
The persistent erythema of the central face should be differentiated from that seen in polycythemia vera, carcinoid, mastocytosis, and connective tissue disease (lupus erythematosus, dermatomyositis, and mixed connective tissue disease).
These conditions do not have associated papules and pustules, will manifest a variety of systemic symptoms and extra facial signs, and specific laboratory markers are available to confirm clinical suspicions. Haber syndrome is a genodermatosis characterised by a rosacea-like facial dermatosis and multiple verrucous lesions on non-sun-exposed skin.
The onset of facial lesions usually occurs during the first two decades of life, in contrast to the later onset of rosacea. While rosacea may occur in human immunodeficiency virus (HIV) disease, a papulonodular eruption of the face that may simulate acne rosacea also occurs in patients with acquired immunodeficiency syndrome (AIDS).