At first, Bian Xiao also thought that the most fundamental reason why the old Beijing foot patch would turn black after being stuck on the sole of the foot overnight was that the foot held its breath, so it would sweat, which would flow into the medicine bag of the foot patch. This medicine bag itself is black and will get wet when mixed with water. This is the truth of dehumidification and detoxification of old Beijing foot stickers. However, after Bian Xiao tried to use it himself, he found that this statement was biased, because when you put it on for the first time, you will find that when you tear it off the next morning, its moisture will spread around the foot patch directly, but if you put it on for a period of time, for example, after a week or a month, the black will not spread around, but will only be concentrated in the middle medicine bag, so it will really help to detoxify. The above is the personal answer to the topic whether the blackening of old Beijing foot stickers really detoxifies. Judging from Bian Xiao's personal experience, the whole person will really feel relaxed after sticking the foot patch, and after sticking it for a period of time, the black on the foot patch will not be so serious, which also shows that people's moisture is not so heavy, indicating that moisture and toxins have been excreted before.