Bifidobacterium longum is a probiotic bacterium commonly found in the human gut. Its use in supporting or treating psoriasis is based on emerging scientific evidence, though the strength of the evidence is still limited. The rationale comes from the increasing recognition of the gut-skin axis, which suggests that the composition of gut microbiota can influence systemic inflammation and immune responses implicated in skin conditions like psoriasis.

Some preclinical studies and small clinical trials have shown that probiotics, including B. longum, may help modulate immune function, reduce systemic inflammation, and improve skin barrier function. For example, a few studies have reported that supplementation with B. longum can reduce pro-inflammatory cytokines and improve markers of inflammation in people with various inflammatory conditions. One pilot clinical trial (J Eur Acad Dermatol Venereol, 2021) found that a multi-strain probiotic including B. longum helped reduce the severity of psoriasis lesions and improved quality of life in patients, though sample sizes were small and results should be interpreted with caution.

Despite these promising findings, high-quality, large-scale clinical trials specifically investigating B. longum for psoriasis are lacking. Therefore, while there is a scientific rationale and some early evidence for its use, the overall strength of evidence is limited at present, and more research is needed to confirm efficacy and establish guidelines for use in psoriasis.