Phellodendron bark (from Phellodendron amurense), also known as Huang Bai in Traditional Chinese Medicine (TCM), has a long history of use for a variety of conditions, particularly those involving "damp-heat" and inflammation. In the context of respiratory allergies, such as allergic rhinitis or asthma, its use is primarily based on traditional practices rather than robust scientific evidence. TCM practitioners may include Phellodendron bark in formulas intended to "clear heat" and "detoxify" the body, which could be interpreted as reducing inflammatory responses associated with allergies.

However, direct evidence for the efficacy of Phellodendron bark specifically for respiratory allergy symptoms is minimal. While some laboratory studies have shown that certain compounds in Phellodendron (such as berberine) possess anti-inflammatory and immunomodulatory properties, clinical trials in humans with respiratory allergies are lacking. The majority of available research focuses on other potential uses, including anti-microbial and metabolic effects.

Therefore, the use of Phellodendron bark for respiratory allergies is justified mainly by traditional use, with limited supportive scientific evidence. The overall evidence rating is low, reflecting a lack of high-quality clinical research specific to allergy management.