The role of altered cutaneous immune responses in the induction and persistence of rosacea.

Rosacea is a chronic inflammatory skin condition that predominantly affects the skin of the face and the eyes. Several factors are associated with the onset and persistence of the condition, including an altered immune response in the skin and elevated levels of Demodex mites. Alterations in the immune response include elevated levels of LL-37 in rosacea skin, increased expression of TLR-2 and increased amounts of vitamin D3 in epidermal tissue. The combined effect of these changes may make the skin more sensitive to external and internal stimuli. External stimuli that may trigger or sustain rosacea inflammation include exposure to ultraviolet light, while internal factors may include the presence of elevated numbers of Demodex mites. These mites may directly stimulate an immune response or release bacteria within the pilosebaceous unit that act as a trigger for inflammation. This review will highlight the changes that occur in the immune response of the skin and describe how Demodex mites and associated bacteria may activate this response and lead to the characteristics of rosacea.