It is not clear whether Amazon's is effective. Through Beijing Science and Education Channel, I learned about a small-particle ecological negative oxygen ion therapeutic instrument, and the effect is good after purchase. The old man can't breathe well and can't cough up thick phlegm. After using this product, the effect is greatly improved, breathing is much smoother, and it is not as uncomfortable as before. I still use it all the time. It is said that the general negative ion therapeutic instrument is completely different from that produced in nature and has the smell of ozone. I have carefully smelled this ecological negative oxygen ion therapeutic instrument, and there is no peculiar smell.