Phaeophyceae, commonly known as brown algae or brown seaweeds (including genera such as Laminaria, Fucus, and Ascophyllum), have attracted scientific interest for their potential anti-arthritic properties, primarily due to their bioactive compounds such as fucoidan, alginates, and phlorotannins. Several in vitro and animal studies have shown that extracts from brown seaweeds can exhibit anti-inflammatory effects. For example, fucoidan has been reported to downregulate inflammatory cytokines (such as TNF-α and IL-6) and inhibit enzymes involved in the inflammatory process, which are relevant to the pathogenesis of arthritis.

However, human clinical trials specifically investigating the effects of Phaeophyceae or their extracts on arthritis are limited and generally of low quality or preliminary in nature. Some small pilot studies and anecdotal reports suggest potential benefits (such as reduced joint pain or swelling), but robust randomized controlled trials are lacking. The traditional use of brown seaweeds for arthritis is not well-documented in ethnobotanical or historical records, and their application seems largely based on modern hypotheses regarding their bioactive constituents.

In summary, the justification for using Phaeophyceae to support or treat arthritis is primarily based on preclinical scientific evidence, but clinical validation is weak. Therefore, the current level of evidence supporting their use in arthritis is limited (rated 2 out of 5).