Editing Rosacea (section)

== Cause ==

[[File:Steroid Rosacea.jpg|thumb|Topical steroid-induced rosacea ''(left)''; after steroid withdrawal and photobiomodulation therapy ''(right)'']]

The exact cause of rosacea is unknown.<ref name="Tuzun2014" /> Triggers that cause episodes of flushing and blushing play a part in its development. Exposure to temperature extremes, strenuous exercise, heat from sunlight, severe [[sunburn]], stress, anxiety, cold wind, and moving to a warm or hot environment from a cold one, such as heated shops and offices during the winter, can each cause the face to become flushed.<ref name="Tuzun2014" /> Certain foods and drinks can also trigger flushing, such as alcohol, foods, and beverages containing [[caffeine]] (especially hot tea and coffee), foods high in [[histamine]]s, and [[spicy food]]s.<ref name=DelRosso2014 />

Medications and topical irritants have also been known to trigger rosacea flares. Some [[Acne vulgaris|acne]] and wrinkle treatments reported to cause rosacea include [[microdermabrasion]] and [[chemical peels]], as well as high dosages of [[isotretinoin]], [[benzoyl peroxide]], and [[tretinoin]].

[[steroid rosacea|Steroid-induced rosacea]] is caused by topical use of  [[steroid]]s,<ref name="urlDermNetNZ">{{cite web |url = http://www.dermnetnz.org/acne/rosacea.html |title = Rosacea |publisher = DermNet, [[New Zealand Dermatological Society]] |access-date = 3 February 2011 |url-status = live |archive-url = https://web.archive.org/web/20101207111722/http://dermnetnz.org/acne/rosacea.html |archive-date = 7 December 2010 }}</ref> which are often prescribed for [[seborrheic dermatitis]]. Dosage should be slowly decreased and not immediately stopped to avoid a flare-up.

=== Cathelicidins ===

In 2007, [[Richard Gallo]] and colleagues noticed that patients with rosacea had high levels of  [[cathelicidin]], an [[antimicrobial peptide]],<ref name="pmid17676051">{{cite journal |author1 = Kenshi Yamasaki |author2 = Anna Di Nardo |author3 = Antonella Bardan |author4 = Masamoto Murakami |author5 = Takaaki Ohtake |author6 = Alvin Coda |author7 = Robert A Dorschner |author8 = Chrystelle Bonnart |author9 = Pascal Descargues |author10 = Alain Hovnanian |author11 = Vera B Morhenn |author12 = Richard L Gallo |title = Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea |journal = [[Nature Medicine]] |volume = 13 |issue = 8 |pages = 975–80 |date = August 2007 |pmid = 17676051 |doi = 10.1038/nm1616 |s2cid = 23470611 }}</ref> and elevated levels of [[stratum corneum]] tryptic [[enzyme]]s ([[KLK5|SCTEs]]). [[Antibiotic]]s have been used in the past to treat rosacea, but they may only work because they inhibit some SCTEs.<ref name="pmid17676051" />

=== Demodex folliculitis and ''Demodex'' mites ===

Studies of rosacea and ''[[Demodex]]'' mites have revealed that some people with rosacea have increased numbers of the mite,<ref name=DelRosso2014 /> especially those with steroid-induced rosacea. [[Demodex folliculitis]] (demodicidosis, also known as "mange" in animals) is a condition that may have a "rosacea-like" appearance.<ref name="Baima2002">{{cite journal |vauthors = Baima B, Sticherling M |title = Demodicidosis revisited |journal = Acta Dermato-Venereologica |volume = 82 |issue = 1 |pages = 3–6 |year = 2002 |pmid = 12013194 |doi = 10.1080/000155502753600795 |doi-access = free }}</ref>

A 2007, [[National Rosacea Society]]-funded study demonstrated that ''[[Demodex folliculorum]]'' mites may be a cause or exacerbating factor in rosacea.<ref name=lacey>{{cite journal |vauthors = Lacey N, Delaney S, Kavanagh K, Powell FC |title = Mite-related bacterial antigens stimulate inflammatory cells in rosacea |journal = [[British Journal of Dermatology]] |volume =  157|issue = 3 |pages = 474–481 |year = 2007 |pmid =  17596156|doi = 10.1111/j.1365-2133.2007.08028.x|s2cid = 8057780 |url = http://eprints.maynoothuniversity.ie/607/1/clinical.pdf }}</ref> The researchers identified ''[[Bacillus oleronius]]'' as a distinct bacterium associated with ''Demodex'' mites. When analyzing blood samples using a peripheral blood mononuclear cell proliferation assay, they discovered that ''B. oleronius'' stimulated an immune system response in 79 percent of 22 patients with subtype 2 (papulopustular) rosacea, compared with only 29% of 17 subjects without the disorder. They concluded, "The immune response results in inflammation, as evident in the papules (bumps) and [[Cutaneous condition#Pustule|pustules]] (pimples) of subtype 2 rosacea. This suggests that the ''B. oleronius'' bacteria found in the mites could be responsible for the inflammation associated with the condition."<ref name=lacey />

=== Intestinal bacteria ===

[[Small intestinal bacterial overgrowth]] (SIBO) was demonstrated to have a greater prevalence in rosacea patients, and treating it with locally acting antibiotics led to rosacea lesion improvement in two studies. Conversely, in rosacea patients who were SIBO-negative, antibiotic therapy had no effect.<ref>{{cite journal |author1 = Elizabeth Lazaridou |author2 = Christina Giannopoulou |author3 = Christina Fotiadou |author4 = Eustratios Vakirlis |author5 = Anastasia Trigoni |author6 = Demetris Ioannides |title = The potential role of microorganisms in the development of rosacea |journal = JDDG: Journal der Deutschen Dermatologischen Gesellschaft |date = November 2010 |pages = 21–25 |volume = 9 |issue = 1 |pmid = 21059171 |doi = 10.1111/j.1610-0387.2010.07513.x |s2cid = 23494211 |doi-access = free }}</ref> The effectiveness of treating SIBO in rosacea patients may suggest that gut bacteria play a role in the pathogenesis of rosacea lesions.