If you maintain your credit balances diligently, owning several credit cards should not tax the existing credit score. However, at a practical level, it really comes down to the financial habits of the user in concern. If the person is careless and incurs debt on multiple cards, there is no question that the credit score will be adversely affected. Conversely, if the user is smart, and uses multiple cards to divide his debts evenly, the credit utilization ratio will be low, which is beneficial for the credit score.