Probiotics are live microorganisms that impart health benefits to the host when present or administered at appropriate levels (J. Appl. Bacteriol. 1989;66:365-78). Intestinal microflora are better understood and more frequently used than cutaneous microbiota, but researchers have recently applied the concepts underlying the efficacy of intestinal probiotics to investigate potential benefits in the dermatologic realm. This work has also been spurred by the flurry of investigations on probiotics for the treatment of atopic dermatitis (AD).
In one of the earlier studies of possible uses of probiotics for the skin, Ouwehand et al. identified strains that adhere to keratin. However, the tested microbes (Propionibacteria, selected because they are among the normal microbiota of the skin) were not found to inhibit cutaneous pathogen adhesion to human keratin. Nevertheless, the researchers concluded that additional study was warranted to identify strains that adhere in vivo and exhibit activity against potential skin pathogens (Lett. Appl. Microbiol. 2003;36:327-31).
Photo courtesy CDC/Janice Carr
Some topical skin products now contain probiotic strains as active ingredients, which incorporate lactobacillus cultures.
Clearly, some probiotic strains have been shown to exhibit strong immunomodulatory activity at the cutaneous level (Eur. J. Dermatol. 2010;20:731-7). In addition, some topical skin products now contain probiotic strains as active ingredients, including Clinique Medical, which incorporates lactobacillus cultures to yield molecules that help ameliorate skin barrier effects from laser treatments or chemical peels (Facial Plast. Surg. 2009;25:285-9). Probiotics have also been used successively as adjuvant therapy to treat suppurative inflammatory conditions (i.e., boils and abscesses) in the maxilla-facial region (Stomatologiia (Mosk) 2009;88:50-2).
This column will consider some of the most current AD studies as well as other recent research. History is not to be disregarded, though. After all, the notion of topical probiotics conferring cutaneous benefits against acne and seborrhea was considered in 1912 (Gut Pathog. 2011;3:1). Current findings may, indeed, bear this out.
Atopic Dermatitis
The safety of probiotic, as well as prebiotic, treatments for AD in children was established in a long-term, randomized, double-blind trial (Clin. Dermatol. 2010;28:57-61; Pediatrics 2008;122:8-1). But questions remain regarding efficacy, with conflicting data emerging from recent studies. Given increasing interest in the use of probiotics for the treatment of AD, Boyle et al. conducted an extensive literature search up to 2008 and found that 12 trials, including 781 subjects (all children), met their inclusion criteria, with probiotics not emerging as an effective treatment for eczema (Cochrane Database Syst. Rev. 2008;CD006135).
In 2008, Betsi et al. reviewed the results of 13 relevant randomized, placebo-controlled trials, 10 of which assessed probiotics as treatment and 3 for prevention of AD. Overall, they found that probiotics, particularly Lactobacillus rhamnosus GG, appear to be effective for preventing AD, lowering its severity in half of the trials assessed though inflammatory markers were not significantly affected. The authors called for more research to determine the usefulness of probiotics in AD treatment or prevention (Am. J. Clin. Dermatol. 2008;9:93-103).
In a 2010 analysis of systematic reviews indexed between August 2007 and August 2008 covering disease prevention and atopic eczema treatment, Williams and Grindlay found two independent systematic reviews suggesting that ingestion of probiotics by mothers during pregnancy might lower the incidence of subsequent eczema. However, they noted that a review of 13 studies of probiotics for treating established eczema revealed no convincing support for its clinical use, a stance that was buttressed by a later Cochrane Review (Clin. Exp. Dermatol. 2010;35:223-7).
In 2010, Gerasimov et al. conducted a randomized, double-blind, placebo-controlled, prospective study of 90 children (1-3 years old) with moderate to severe AD treated with a mixture of L. acidophilus DDS-1 and Bifidobacterium lactis UABLA-12 with fructo-oligosaccharide (5 billion colony-forming units twice daily for 8 weeks vs. placebo). The researchers found that the use of the probiotic compound correlated with significant clinical improvement in children with AD, and suggested that additional research is necessary to assess the efficacy of probiotics in adults with AD (Am. J. Clin. Dermatol. 2010;11:351-61).
In another recent study, investigators isolated L. plantarum strains from the Korean fermented food kimchi, and found that they hindered the dermatitis promoted by house-dust mites in a mouse model representative of human AD (J. Appl. Microbiol. 2011;110:1195-202). Overall, clinical trials conducted to test the use of probiotics to treat AD over the last 15 years have yielded conflicting results, though it appears that there is not enough evidence to warrant support for such therapy (Clin. Rev. Allergy Immunol. 2011;41:267-71).
Mechanism of Action
Presently, the mechanism of action whereby skin benefits are manifested through the oral ingestion of probiotics is thought to be a downstream result of the boost in systemic immune response, especially T-cell subsets such as Th1 cells that may ultimately enhance immune responses in organs beyond the digestive tract (Clin. Plast. Surg. 2012;39:59-64; Clin. Dermatol. 2008;26:4-11).