NEW YORK — When a major bank’s credit rating is cut, it deals a psychological blow — to customers, the public, and financial markets.

So Thursday’s downgrading of 15 of the world’s largest banks is almost sure to cause wide concern. Most deposits are perfectly safe, but the downgrades could hurt people in more subtle ways: Banks may jack up fees and be reluctant to lend, which could affect mortgages, credit cards, and even the job market.

The downgrades could eventually increase the banks’ cost of borrowing in financial markets because investors will demand more interest when they lend the banks money. With interest rates hovering near record lows, most analysts say the cost of borrowing will not be affected immediately. However, if the ratings remain at these levels and interest rates rise, banks will pay dearly.

For now, investors are not worried. The stocks of downgraded banks rose Friday. Bank of America gained 1.5 percent, while JPMorgan Chase and Morgan Stanley each rose 1.3 percent.

The downgrades also suck capital out of banks. That’s because all the large banks sell insurance to investors to protect them from losses on bonds in case of a default.

The downgrades will force banks to set aside billions of dollars in additional reserves because the debt they are insuring has become riskier. Each notch in the ratings scale triggers automatic requirements for additional money a bank must set aside in reserves.

Because of those requirements, the downgrades will funnel money into reserves and reduce the amount of capital that banks have to lend.

Americans will experience it when they go to their banks for home mortgages, car loans and credit cards.