Here is a simplified explanation for choosing formulas with suspected allergies/ intolerances. Formulas have two main ingredients(besides water)- sugar and protien. Lactose is the main sugar in breastmilk and cows milk, sucrose and corn syrup are in soy milk and the hypo-allergenic formulas. Cow protiens are in cows milk, soy protiens in soy milk, and chemically or heat altered or broken down protiens are in the Nu--------n et al. Allergies are a response to foreign protiens. Lactose problems are usually due to enzyme (lactase) deficiencies. The gut cannot completely break down the lactose or other disaccharides (two part sugars). Resulting in gas, diarrhea, pain, or bloating. Most problems are a relative problem, not a complete lack of the needed enzymes. The enzyme needed for lactose is highest in infants and declines with age. Depending on the ethnic group 20-80% of adults cannot digest lactose well. I still cannot figure out what lactose-free cows milk formula is for. Congenital lactase deficiency is very very very rare. In spite of what we were once taught acquired lactase deficiency in infancy does not occur in most cases of simple or moderate diarrhea. If a baby does well on breast milk, but not cows milk formula the problem cannot be lactose. Dairy in mom's diet would not change the lactose content, but might alter the protiens. When I switch formulas in suspected allergic infants, I use a non-cow/ non-soy ABM because there seems to be a bit of overlap between cow and soy protiens. I always tell the parents to give the baby at least a week after the change. Sometimes I think I am just buying time until the baby's gut matures a bit, the parents calm down, or the baby outgrows her colic. I do have a few truly allergic infants who develop hives and swelling with the ingestion of cow milk protiens, otherwise I suggest they go back to a less expensive formula after 3-4 weeks. Most infants tolerate cows milk by age one even if they had a lot of symptoms on cows milk as infants. Mary Murphy MD