Houttuynia cordata, commonly known as "fish mint" or "chameleon plant," has a long history of use in traditional East Asian medicine. In systems such as Traditional Chinese Medicine (TCM) and Korean folk medicine, Houttuynia is believed to have "heat-clearing" and detoxifying properties, and is sometimes used topically or internally to address skin conditions, including eczema (atopic dermatitis). Documented uses include poultices, washes, or oral preparations, often in combination with other herbs.

Scientific studies specifically investigating Houttuynia’s efficacy for eczema are limited and mostly preliminary. Some in vitro and animal studies have indicated that Houttuynia extracts possess anti-inflammatory, antioxidant, and antibacterial effects, which could theoretically be beneficial for inflammatory skin conditions. However, robust clinical trials in humans for eczema are lacking. Thus, while its traditional use for treating eczema is established, scientific validation for this specific indication remains insufficient.

In summary, the use of Houttuynia for eczema is primarily justified by tradition rather than strong scientific evidence. The evidence rating reflects the presence of some supporting data from basic research and historical use, but a lack of well-designed clinical trials.