Aureobasidium pullulans is a species of black yeast that has gained attention in recent years for its ability to produce beta-glucans, particularly the beta-1,3-1,6-glucan known as beta-glucan or APβG. These beta-glucans have demonstrated immunomodulatory, anti-inflammatory, and antioxidant properties in various preclinical and limited clinical studies. In the context of psoriasis, a chronic, immune-mediated inflammatory skin disorder, the rationale for using A. pullulans-derived beta-glucan is largely based on its potential to modulate immune responses that drive the disease, such as the Th1 and Th17 pathways and the production of pro-inflammatory cytokines like TNF-α and IL-17.

While several in vitro and animal studies suggest that APβG can reduce inflammatory cytokine production and oxidative stress, direct evidence from human clinical trials in psoriasis patients is limited. There are a small number of pilot studies and case reports suggesting some benefit in reducing psoriasis severity scores and improving skin symptoms, but these are preliminary and often lack rigorous controls or large sample sizes. There is also no established traditional use of A. pullulans for psoriasis; its application is a recent development grounded in modern immunology.

In summary, the use of A. pullulans for psoriasis is justified by early scientific investigation into its beta-glucan's immunomodulatory effects, but the current clinical evidence base is limited, warranting a modest evidence rating of 2 out of 5.