A single credit card application won’t hurt your credit score much. But if you apply for multiple cards within a short period of time, that may ruin your score significantly. Your credit score may be affected because every time you apply for a credit card or a loan, the lender reviews your credit report. This is known as a hard inquiry. They may stay in your credit report for up to two years. The more inquiries you have on your credit report, the more risky you are considered. Also, people with a short credit history and a low credit score risk the greatest impact from inquiries.