Co-signing a loan involves risks such as assuming full payment responsibility, damaging your credit, impacting your ability to get future credit, facing legal issues, possibly losing property, and harming personal relationships. It's advisable to co-sign only if you can afford the risk, it benefits both parties, or you genuinely want to help the borrower. Alternatives include helping with a down payment or lending money directly. To protect yourself as a co-signer, communicate with the lender and borrower, track payments, and manage risk by preferring smaller, short-term loans.