All fuels are unleaded. There is no harm with regular. Only thin, if you use premium, use it only. Do not mix it with regular.?

Ethanol has replaced lead as an anti knocking, (higher compression ratio,) additive. Ethanol is not allowed in fuel for airplanes and boats.

All gasoline is harmful as a liquid and after it is burned. The question is how much. Don't drink it or get too much of it on your skin, don't breath the fumes before or after it is burned.

Only thin?

Premium is not a better gasoline in every situation. It is made for a higher compression ratio. Follow the mfg recommendations.

If your car needs premium don't use regular. If your car can use regular why spend more for premium that you don't need?

Where do you think they get mid grade gas when there is no tank for it at most gas stations. Many gas stations just mix regular and premium in the pump to make mid grade.

As for whether premium would do you any good, we have answered this question hundreds of times. In the search window above type in:

regular vs premium

And click "Search Answers"

Nope. If you buy midrange gasoline, you are getting a blend of premium and regular. Buy whatever grade your vehicle runs best on.

they can be mixed.

i think so