Is it possible for a baby to do well on similac advanced and at 7 weeks develop an allergy? will he grow out of it? could it be something else?

Food Allergy: It is surely possible. It could be either a true milk/dairy allergy or it could simply be lactose intolerance. Easiest treatment is to switch to a soy-based formula and/or ask your doctor to check a rast level to cow's milk.

Rare but possible: A kid with true milk allergy will have it long term. Most do not. Many on a lactose based milk formula can develop transient lactose intolerance with routine stomach viruses and benefit from lactose free formula for a week or so until it self heals.Many also have imbalance of gut germs and benefit from gogert or other product to realign their digestion.

Possible: It is possible to develop an allergy. however, without knowing your child's symptoms, it is hard to say if it is an allergy or not. Milk protein intolerance identified in the first three months of life is often outgrown by 12 months.