Should gloves be worn when working with concrete to prevent it from coming in contact with skin?
Cement (the active component of concrete) is a base (an alkali) that can be irritating to skin. It is not very strong and should not be a problem on all but sensitive skin, if the exposure is short or intermittent. It could be very irritating to eyes and nasal passages if there is a lot of exposure.

Gloves are not a bad idea (e.g., disposable nitrile) but concrete pourers and DIYers handle all the time with little ill effect (again, for short exposure).