Chrysanthemum maximum, commonly known as Shasta daisy, is not widely documented in either traditional medicine or scientific literature for the treatment of conjunctivitis specifically. However, related species within the Chrysanthemum genus, particularly Chrysanthemum morifolium (commonly known as "Ju Hua" in traditional Chinese medicine), have a long history of use in East Asian herbal medicine to address eye-related ailments, including conjunctivitis and eye inflammation. The rationale for their use is based on traditional beliefs that certain chrysanthemum species have "cooling" and anti-inflammatory properties, which can help alleviate redness and irritation of the eyes.

There is a paucity of scientific research specifically investigating Chrysanthemum maximum for conjunctivitis. Most available evidence is anecdotal or based on traditional herbal compendia referencing the broader genus. Some laboratory studies on related Chrysanthemum species suggest the presence of bioactive compounds with anti-inflammatory and antioxidant effects, which could theoretically support their traditional use for inflammatory conditions. Nonetheless, no clinical trials or controlled studies have directly evaluated Chrysanthemum maximum for conjunctivitis in humans.

In summary, the use of Chrysanthemum maximum for conjunctivitis is primarily supported by traditional practices—largely extrapolated from use of related species—and lacks robust scientific validation. The level of evidence is weak, and caution should be exercised in interpreting its potential efficacy for this condition.