Many public toilets have colored balls that change the smell, so please ask

That's a health ball, the main ingredient is naphthalene, no harm, no.

Haven't seen it.

One I know is that bamboo charcoal, activated carbon and the like have strong adsorption, absorb odors, and have no effect on the human body. There is also a scented Dongdong, which is generally esters or other organic ingredients to mask the odor; It may also have some odor-absorbing ingredients added to it. >>>More

If you are talking about the kind that comes in a mesh bag, it is a mothballs with added pigments, which are generally synthetic, containing naphthalene or dichlorobenzene, and have a pungent smell; Dichlorobenzene is toxic, and it can cause human poisoning symptoms, such as fatigue, dizziness, headache, diarrhea, etc. >>>More

The new mothballs are colorful and good-looking.

Definitely not, to put it simply, there are so many people in China. If you can get infected, the consequences are unimaginable.