K.B.
Are you talking about taking a loan from an active retirement account that will be paid back through deductions from your paycheck? If so, then the only thing you have to be aware of is that if for any reason while the loan is outstanding you no longer are employed by the company you will be responsible for paying the loan back or you will have to pay the income tax plus penalty tax for the outstanding amount. As long as you are employed and the payments are coming from your paycheck you do not pay any additional income tax or penalty taxes on the money.
The one taxation issue that some people get hung up on is the idea that the money was originally put into the account on a pre-tax basis but when you pay it back it will be after tax. Even though the repayments will be after tax, when you withdraw the money again once you retire you will be taxed. Some don't like the fact that you do get taxed on this money twice, but you are being allowed to use the money twice so it balances. All depends on how you look at it.