Rosmarinic acid is a polyphenolic compound found in various medicinal herbs, most notably in rosemary (Rosmarinus officinalis) and lemon balm (Melissa officinalis). Its use in supporting or treating dermatitis is primarily justified by emerging scientific evidence, although the clinical data is still limited and mostly preclinical. Rosmarinic acid exhibits notable anti-inflammatory, antioxidant, and immunomodulatory properties, which are relevant to the pathophysiology of dermatitis.

In animal studies, topical or oral administration of rosmarinic acid has been shown to reduce skin inflammation, decrease edema, and suppress cytokine release in models of atopic and contact dermatitis (Osakabe et al., 2004). These effects appear to be mediated through inhibition of pro-inflammatory mediators such as TNF-α, IL-1β, and histamine, as well as by reducing oxidative stress in the skin. Some small-scale human studies and case reports suggest that topical formulations containing rosmarinic acid may help alleviate mild symptoms of dermatitis, but rigorous clinical trials are lacking.

In summary, while there is promising preclinical and some early clinical evidence supporting the use of rosmarinic acid for dermatitis, more robust human studies are needed to establish its efficacy and safety. As such, the evidence base is moderate (rated 3/5), with most support coming from laboratory and animal model research.