Although a pediatrician says it's safe to start at 4months, a baby's gut cells don't fully close til 6months of age. So waiting til 6months is a safer way to ensure their gut doesn't mess up.
My pediatrician said we can start at 4 months so we did. The only 2 brands our store had was Gerber and Beech-Nut. We used Beech-Nut because we liked it better 😊