Results of two recent studies provide new understanding of how and when angiogenesis -- the formation of new blood vessels -- may contribute both to the initial development of rosacea and its persistent presence.
In a study of skin samples with and without rosacea, Dr. Amal Gomaa and colleagues at Boston University found evidence of angiogenesis in both the blood and lymphatic circulatory systems in skin with rosacea lesions. 
While the development of visible blood vessels, called telangiectasia, has long been recognized in rosacea, evidence of lymphatic vessel growth has not been previously reported, the researchers said. They also noted that study results suggested lymphatic involvement occurs at the beginning of the disease rather than later in its progress. The lymphatic circulatory system consists of vessels that carry a clear liquid that bathes the tissues of the body and may fight infection.
"Our study may highlight new players in the pathogenesis of rosacea," the researchers said in the article. They pointed out that the lymphatic angiogenesis was not expected as no patient had facial swelling, but that the findings support the long-held belief that the lymphatic system is involved in the process of skin inflammation.
The researchers also noted that increased expression of vascular endothelial growth factor (VEGF), which plays a role in angiogenesis, was found only in rosacea-affected skin samples. Interestingly, the study found no difference in VEGF levels between subtype 1 (erythematotelangiectatic) rosacea, characterized by facial redness, and subtype 2, (papulopustular) rosacea, characterized by bumps and pimples, which suggests that telangiectasia may be present in each.
In another study of affected and unaffected skin, Dr. Kyriaki Aroni and colleagues of the University of Athens studied the potential role of angiogenesis and mast cells in rosacea. 
"It seems increasingly possible that rosacea pathology is a multifactorial process, which opens up areas of research with regard to potential links between different contributing factors," the researchers said. Mast cells, connective tissue cells that release chemical substances in response to injury or allergic reaction, are known to augment inflammatory processes and occur in increased numbers in conditions associated with angiogenesis.
In their study of 69 rosacea patients, the researchers found that the number of mast cells was significantly higher in skin with rosacea, especially later in the disease, suggesting that the cells may be involved in the longer duration of rosacea. They pointed out that rhinophyma (enlargement of the nose), usually a later manifestation of rosacea, is also characterized by increased numbers of mast cells.
1. Gomaa AHA, Yaar M, Eyada MMK, Bhawan J. Lymphangiogenesis and angiogenesis in non-phymatous rosacea. Journal of Cutaneous Pathology 2007;34:748-753.
2. Aroni K, Tsagroni E, Kavantzas N, Patsouris E, Ioannidis E. A study of the pathogenesis of rosacea: how angiogenesis and mast cells may participate in a complex multifactorial process. Archives of Dermatological Research DOI: 10.1007/s00403-007-08162.