Soap and water is the best way to wash your hands you can use hand sanitizer after if you wish but if you skip washing your hands regularly then hand sanitizer is a useless endeavor and would be bad for you if you use it to replace washing.

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As for hand sanitizer itself, its main ingredient is alcohol which dries out the skin with frequent use your skin on your hands can have symptoms of premature aging.

The immune system it may seem counter-intuitive but we actually need germs in day to day life to have a healthy immune system there is a certain level of germs that is quite healthy to be around when you eliminate all germs from your environment your immune system becomes weaker and functions less leaving you at risk of contracting infections and viruses.

Chemicals at the end of the day hand sanitizers have a lot of chemicals in them especially if they are fragranced such as parabens that are not healthy for the body.

Using too much of anything is bad for you use it in moderation and make sure to also wash your hands when you can unless it's cold and flu season or you around people you are at risk of contracting something from.

Update!

*I wrote this answer before the coronavirus pandemic

I still stand by my answer but given the current circumstances, I feel I should elaborate when speaking about the immune system and how its good to be around a certain level of germs so the immune system remains strong that was a precautionary thing to do under normal circumstances excluding washing hands after going to the bathroom or before and during food preparation obviously!.

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Now that the coronavirus is in full swing, please use hand sanitizer frequently after touching any services shared by others if you don't have access to soap and water and a private basin that is not shared by the public. While hand sanitizer does not cleanse the skin of dirt it does kill bacteria and viruses on the skin, it kills the coronavirus specifically by breaking down the fatty layer encasing the virus and then killing the virus itself.

So to summarize frequent hand washing with soap and water is better, but if you are in public and lack access to a private basin hand sanitizer is the way to go just wash your hands as soon as you can.