In addition to improving the clinical signs of rosacea, topical ivermectin, an FDA-approved antiparasitic agent for papulopustular rosacea, also may be effective because it alters the bacterial composition of the skin, according to a recent National Rosacea Society-funded study in the Journal of Investigative Dermatology.1
“In this study, we provide evidence that topical ivermectin not only decreases the density of Demodex but also affects the bacterial community on the skin of rosacea patients,” said Dr. Tissa Hata, the study’s lead researcher.
Daily treatment with 1% topical ivermectin cream decreased the redness as well as the number of papules on the facial skin of 10 patients with papulopustular rosacea, according to the report. The 12-week study included 10 age-matched healthy control subjects for baseline comparisons.
Ivermectin may also have improved rosacea by altering the facial microbiome – the number and diversity of the bacteria present on the skin, Dr. Hata said.
Demodex, a microscopic mite that is a normal inhabitant of healthy skin, has often been found in 15 to 18 times greater numbers in rosacea patients than in healthy subjects.2 The action of ivermectin against Demodex is believed to be substantial, the researchers said, but they also noted that the role of the mites as the sole driver of rosacea has been unclear.
An imbalance of the microbiome, known as dysbiosis, has been observed on the skin of patients with rosacea, though the reasons for this imbalance are still largely unknown, she said. Demodex frequently co-infects the skin with various bacterial pathogens,1 the researchers noted, and in addition to an increased number of Demodex on skin with rosacea lesions, the bacteria Cutibacterium acnes and Staphylococcus epidermidis were found on affected and non-affected skin of both patients and controls before therapy.
After treatment, while ivermectin decreased the number of Demodex mites and the amount of C. acnes showed no change, the S. epidermidis population on the facial skin increased. Certain strains of S. epidermidis may be beneficial in that they are anti-inflammatory,1 the investigators said, and some produce their own antimicrobial substances, which can suppress the overgrowth of pathogenic bacteria.
Rosacea is also characterized by an overproduction of the antimicrobial peptide cathelicidin,3 they noted, and in a related study,4 the investigators found that this increase depletes the beneficial antimicrobial strains. However, treatment with ivermectin inhibits the expression of cathelicidins, they said, and thus indirectly promotes the anti-inflammatory effects of the beneficial bacteria.
“Alteration of the microbiome with these beneficial strains may further improve the inflammatory homeostasis in rosacea,” they said.
As the beneficial or detrimental functions of the skin’s bacteria are dependent on which particular strains of bacteria are present, larger additional studies are necessary to fully understand the effects of ivermectin on the functions of the skin microbiome, they said.
Since its founding, the National Rosacea Society's research grants program has awarded more than $1.7 million to researchers for a wide range of rosacea-related studies, and the program is funded by donations from many thousands of individuals who wish to improve the lives of those affected by rosacea. Join the fight against rosacea. Donate to this important program today.
References:
1. Nakatsuji T, Cheng JY, Butcher A, et al. Topical ivermectin treatment of rosacea changes the bacterial microbiome of the skin. J Invest Dermatol 2024 Oct 29:S0022-202X(24)02869-0. doi: 10.1016/j.jid.2024.10.592. Epub ahead of print. PMID: 39481532.
2. National Rosacea Society. The ecology of your face: Demodex, rosacea and you. https://www.rosacea.org/patients/the-ecology-of-your-face-demodex-rosacea-and-you Accessed January 24, 2025.
3. Yamasaki K, Di Nardo A, Bardan A, et al. Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea. Nat Med 2007 Aug;13(8):975-80. doi: 10.1038/nm1616. Epub 2007 Aug 5. PMID: 17676051.
4. Nakatsuji T, Brinton SL, Cavagnero KJ, et al. Competition between skin antimicrobial peptides and commensal bacteria in type 2 inflammation enables survival of S. aureus. Cell Rep 2023 May 30;42(5):112494. doi: 10.1016/j.celrep.2023.112494. Epub 2023 May 10. PMID: 37167061; PMCID: PMC10303920.