Humic acid, a mixture of complex organic molecules derived from the decomposition of plant material, has been studied for its antiviral properties. Some in vitro (test tube) studies have shown that humic acid and related substances can inhibit the replication of herpes simplex virus (HSV), which is responsible for cold sores. For example, research published in the journal Antiviral Research (Zhernov et al., 2021) and other studies from the 1990s and early 2000s have demonstrated that humic acid derivatives can block HSV-1 and HSV-2 infection in cell cultures, possibly by interfering with viral binding to host cells or viral entry mechanisms.

However, the clinical evidence in humans is limited. There are very few, if any, well-controlled human trials examining the effectiveness of humic acid for the treatment or prevention of cold sores. Most evidence remains preclinical and is not sufficient to support widespread clinical use. Humic acid is not a standard or widely recognized therapy for cold sores in conventional medicine. Its use is primarily based on early laboratory research and some anecdotal or alternative medicine reports, rather than on robust clinical validation.

In summary, while laboratory studies suggest humic acid has antiviral potential against HSV, the current evidence for its use in treating cold sores in humans is weak (rated 2/5), and more research is needed to determine its efficacy and safety in clinical settings.