Impact Of Probiotics On Gut & Skin Microbiome In Psoriasis

What is Psoriasis?

Psoriasis is a systemic immune-mediated inflammatory skin condition affecting approximately 8 million people in the U.S. and 125 million people worldwide that results from a combination of genetic and environmental factors.^[1] It causes the body to make new skin cells in days rather than weeks, resulting in thick scaly patches. Most people who develop psoriasis have it for life.  Though psoriasis is not curable, there are many strategies to gain control of the condition and prevent worsening. Popular ones include medications like topical corticosteroids and retinoids, salicylic acid, coal tar, immunosuppressants, and biologics. Equally important is avoiding environmental triggers like stress, smoking, alcohol, and certain foods.

The Gut Microbiome in Psoriasis 

Changes in the microbiome have been associated with several systemic and immune-mediated conditions such as asthma, atherosclerosis, metabolic disorders, irritable bowel syndrome, and inflammatory bowel disease.^[2-5] Though data on the gut microbiome in skin conditions like psoriasis are limited, we are beginning to understand that gut bacteria may trigger inflammation outside the gut. For example, a 2018 study conducted by Codoner et al.^[6] using 16s rRNA sequencing found that the intestinal microbiome composition in psoriatic patients showed a defined microbial structure labelled as the “psoriatic core intestinal microbiome” that differed significantly from healthy people. In other words, patients with psoriasis demonstrated a more “inflammatory microbiome fingerprint.” Specifically, they found an increase in Faecalibacterium, which has been implicated in pro-inflammatory disorders such as inflammatory bowel disease,^[7] eczema,^[8] and atopic dermatitis,^[9] and a decrease in Bacteroides, which was also found at lower levels in infants with eczema.^[8] These data suggest a microbial imbalance or “dysbiosis” which may promote a pro-inflammatory state in individuals with psoriasis.

The Skin Microbiome in Psoriasis

The skin microbiome is colonized by a diversity of microorganisms highly variable depending on one’s diet, environment, genetics, and a host of other factors. Recent studies suggest that the skin microbiome composition may play a crucial role in maintaining the integrity of the skin, affecting dermatologic conditions like psoriasis. There are four major genera typically found on the skin:

• Cutibacterium
• Corynebacterium
• Streptococcus
• Staphylococcus

Patients with psoriasis demonstrate an imbalance in the abundance of these four major genera compared to healthy controls. For example, one study demonstrated an increased abundance of Streptococcus with a decreased abundance of Cutibacterium in patients with psoriasis compared to healthy populations.^[10] Two studies demonstrated an overrepresentation of Staphylococcus aureus and an underrepresentation of Staphylococcus epidermidis and Cutibacterium acnes in both lesional and non-lesional psoriatic skin.^[11,12] As Cutibacterium acnes and Staphylococcus epidermidis are considered dominant organisms in normal healthy skin that help provide immunoregulatory functions,^[13] a reduction in their numbers may lead to higher colonization of more pathogenic bacterial strains like Staphylococcus aureus that could exacerbate or contribute to the pathogenesis of psoriasis.

Alekseyenko et al. looked at 75 patients with psoriasis and showed an increase in abundance of Corynebacterium, Streptococcus, and Staphylococcus compared to healthy controls in both lesional and non-lesional psoriatic skin.^[14] These results (Table 1) contribute to the theory that psoriasis is associated with a systemic change in the skin microbiome. 

How do Probiotics Help Psoriasis? 

Probiotics are live microorganisms with the ability to confer many health benefits by restoring balance to the microbiome. There is a growing body of research focusing on the use of probiotics in the prevention and treatment of certain dermatologic diseases such as atopic dermatitis.^[15] Though there are few studies that focus specifically on the use of probiotics in psoriasis, it is theorized that probiotic therapies may be able to balance a person’s pro-inflammatory and anti-inflammatory immune functions by promoting good bacteria that reduce inflammation in psoriasis.   

Which Probiotics Help Treat Psoriasis?

The most common microorganisms used in probiotics are:^[16]

• Lactobacillus
• Bifidobacterium
• Enterococcus
• Cutibacterium
• Saccharomyces boulardii yeast

Many studies looking at oral probiotics that include Lactobacillus and Bifidobacterium have been shown to help prevent and treat inflammatory skin conditions like atopic dermatitis.^[17] Though there is limited research (Table 2) on which strains of probiotics help treat psoriasis specifically, one study of 26 patients with psoriasis compared the effect of oral probiotic Bifidobacteirum infantis 25634 on proinflammatory markers in psoriasis and found levels of C-reactive protein and tumor necrosis factor (TNF)-alpha declined significantly after 8 weeks of therapy compared with placebo and baseline.^[18]

Additionally, an in vivo study found that oral administration of Lactobacillus pentosus GMNL-77 significantly decreased proinflammatory cytokine mRNA levels (IL-6, TNF-a, and IL-23/IL-17A) and decreased skin erythema and scaling in the skin of mice with imiquimod-induced psoriasis-like inflammation.^[19]

One case report of a patient with pustular psoriasis nonresponsive to steroids and methotrexate showed that oral administration of Lactobacillus sporogenes three times a day over 6 months treated her acute lesions within 2 weeks with no recurrence of new lesions.^[20]

A survey conducted on 1206 psoriasis patients looking at dietary habits, interventions and modifications found that 40.6% of patients of all surveyed reported improvement or full clearance after adding probiotics to their diet.^[21]

RCT = Randomized Control Trial

Do Topical Probiotics Work? 

Probiotics can influence the composition of the skin microbiome when applied topically.  Through the fermentation process, probiotic bacteria make acidic byproducts like lactic acid which can reduce the pH of the skin.^[22] Since skin prefers a naturally acidic environment, these byproducts can modulate the skin, limiting the growth of pathogenic bacteria and favoring the growth of bacteria that naturally reside on the skin. Furthermore, probiotic bacteria are capable of producing antimicrobial products like bacteriocidins that prevent the adhesion of pathogenic bacteria.^[23]

There is little data regarding the use of topical probiotics in the treatment of psoriasis. However, there is evidence that topical probiotic use can improve the general health of skin.  One study showed that topical application of Lactobacillus plantarum was found to reduce erythema and improve the skin barrier in patients with acne. Another study by Khmaladze et al. found that both live and lysate products of Lactobacillus reuteri DSM 18938 reduced proinflammatory IL-6 and IL-8 markers and live L. reuteri had antimicrobial action against pathogenic skin bacteria including Staphylococcus aureus, Streptococcus pyogenes, Cutibacterium acnes, and Pseudomonas aeruginosa.^[24]

While further investigation is needed before making definitive recommendations on both the oral and topical effects of probiotics in patients with psoriasis, these studies contribute to a growing interest in the gut-skin axis and potential therapies that can benefit patients.

Take Home Points

• There is limited but promising evidence that both the gut and skin microbiomes in patients with psoriasis differs significantly from healthy populations with potential for a “psoriatic microbiome”

• To date, two prospective studies, one case report, and one survey suggest that treatment of psoriasis with oral probiotics including Lactobacillus and Bifidobacterium strains may help improve symptoms and decrease inflammation