Many cow's milk-intolerant children experience very delayed reactions to a cow's milk challenge. The following summarizes the results of a recent study.

• Cow's milk challenge tests were conducted 12 months after institution of cow's milk-free diets in 86 children with cow's milk intolerance.
• 10 out of the 86 patients showed "very delayed reactions" to a cow's milk challenge averaging over 13 days (range 4-26 days).
• These "very delayed" reactions included constipation, wheezing, and dermatitis.
• All symptoms in these children disappeared after reinstitution of a cow's milk-free diet.
• Delayed reactions to cow's milk may be misdiagnosed if the symptoms are not "classical" and there is a long time lapse between ingestion the reaction.
• 30% of the children became cow's milk-tolerant within 1 year after their diagnosis.
• By years 2 and 3, 55% and 70% of the children, respectively, were cow's milk-tolerant.

In light of their findings, the authors conclude, "We feel that after a standard cow's milk challenge [1-week challenge], a careful follow-up and frequent outpatient observation of the reintroduction of cow's milk in the diet in patients with a long history [of cow's milk intolerance] are more useful and safer than prolonged cow's milk challenge."

Allergy 2000;55:574-9