Dear Liz: I’ve read that adding a child as an authorized user on your credit card could help build his or her credit history. But I was specifically told that this was not the case, as the child’s Social Security number was not primary.

Answer: Whoever told you may not have understood how authorized user activity typically is reported, or may have been talking about a specific issuer’s policy.

Adding someone as an authorized user to a credit card typically results in the history for that card being added to the authorized user’s credit report. That in turn can help the authorized user build credit history and improve his or her credit scores.

Some smaller issuers, such as credit unions or regional banks, may not report authorized user activity to the three credit bureaus, but all of the major credit card companies do. Some of these big issuers, however, don’t report the information if the authorized user is younger than a certain age or if the information is negative. The age cutoff varies by issuer. For American Express and Wells Fargo, for example, it’s 18; for Barclays, it’s 16 and for Discover, it’s 15. Other major issuers don’t have an age cutoff. American Express and U.S. Bank also won’t report to the authorized user’s credit file if the account is delinquent.

The credit bureaus, in turn, have their own policies. TransUnion includes whatever the issuers report. Equifax adds the information to the credit report if the authorized user is at least 16. Experian adds the information supplied by the issuers, regardless of age, but will remove it if the original account becomes “derogatory” — which typically means payments are skipped or the account is charged off.

If you want to help a child build credit by adding the child as an authorized user, you’ll want to make sure you’re adding him or her to a card that will actually do some good. A quick call to the issuer can help you find out its policy on reporting authorized user activity.