How do i know if my baby has an allergy from a tcertain type of food? is there a specific test that can be done once for all foods?

No universal test: Testing is rarely 100% accurate & i know of no universal tests for food allergies.Some labs have a variety of blood studies that correlate with some food reactions, but allergists usually pair the blood study with pin prick tests. All of which can falsely suggest allergy. Sometimes just eliminating the material from the diet for 2 wks, seeing benefit, & seeing pbs if restarted tells u.