Having unauthorized user on your credit report will not have an effect on your credit score even if the authorized user has a poor credit history.

All credit histories are maintained on an individual basis and only the accounts that are jointly held included both the joint account holders credit reports.

The only effect of having unauthorized user on your credit card will be the inclusion of the concerned account in the authorized users credit report. No inclusion of their credit report or any other kind of association will be made in your credit history as the primary credit card holder.

As to whether or not the inclusion of the authorized account in the credit history of the authorized user will help his/her credit score, the answer is no.

Credit scoring model is no longer considered authorized user accounts in the calculation of the credit score. Owing to the views of authorized user accounts in the past with the practice called piggybacking where one would take advantage of a person’s good credit report to boost their own, the credit score is no longer include data from the authorized user accounts when determining a consumer’s credit score.

While the poor history of unauthorized user will not impact your credit history the risk comes in the fact that the authorized user might make the charges that he or she cannot afford to pay back the thing you liable to make the payments. In case these payments go unpaid and are reported as late than that information will find its way on your credit report and hurt your credit scores.