This association is mild, however, and only applies to a minority of newborns with Colic. Babies with food allergy may initially seem to have Infant Colic - however they will usually develop other symptoms of food allergy within a few weeks time. These other symptoms can include eczema, spitting up, diarrhea, bloody stool, and a failure to grow. The development of these other symptoms makes the diagnosis of food allergy easy once they occur - and they do eventually occur in almost all babies who have food allergy. Because hypoallergenic formulas are very expensive and not as nutritionally complete as the more standard infant formulas, however, switching colicky infants to them before they have developed other signs and symptoms of allergy is not generally recommended.
Lactose intolerance is an inability to digest the main sugar in milk.
It is NOT a food allergy and bears no relationship to food allergy. It tends to run in families and can sometimes present initially as Infant Colic. However, newborns with Lactose intolerance tend to have other symptoms beyond crying - particularly spitting up and poor growth. Likewise, simple Constipation can also present with Colic - but usually this is obvious because the child has firm stools. Thus, both Lactose Intolerance and Constipation are usually fairly easy to recognize, and respond to simple interventions such a change in formula or a stool softener.