According to Experian:

Absolutely. By cosigning, you are accepting full responsibility for the debt if the other person does not pay as agreed. A cosigned account will appear on both your credit history and the other person’s. All loans and credit card accounts that appear on your credit report will impact credit scores.

According To Experian:

Having too many credit cards with either high balances or large amounts of credit available can negatively impact risk scores depending on the overall credit history.