Heartleaf

Heartleaf (Houttuynia cordata) contains volatile oils, flavonoids, alkaloids and polyphenols [2]. Its fishy smell comes from a compound called decanoyl acetaldehyde, which disappears when the herb is dried [5]. The raw plant readily takes up lead and cadmium from soil, a quality-control point for manufacturers rather than a known product risk [2].

The one human trial is small but well designed. In a Thai randomised, placebo-controlled study, 16 adults used a toner containing 0.05% heartleaf extract or an identical toner without it every morning for eight weeks. The heartleaf group's sebum fell about 4.6 times more than placebo and cheek hydration was about 1.4 to 1.5 times higher, with no side effects. It was funded by a Thai government research agency, not a brand [1].

The calming reputation comes from the lab: fermented heartleaf broth turned down inflammatory and cell-death signals in human skin cells, and fermented broth outperformed unfermented. The researchers caution that this 'does not guarantee the same level of safety when applied to humans' [3]. A US safety review found no published human irritation or sensitisation studies [2].

Its folk history is long. In Japan the crude drug is called juyaku, 'ten medicines', it is listed in the Japanese Pharmacopoeia, and dokudami tea is still popular [5]. In Korea it's called eoseongcho, 'fish-smell herb', and grows wild on Jeju [4].

Its fame now comes from one product: Anua's Heartleaf 77% Soothing Toner, where heartleaf water is 77% of the formula [6]. Brand figures such as 'sebum decreased by 49.55%' come with no published sample size [6]. The 77% plant water and the trial's 0.05% extract aren't comparable numbers.