The aim of the study is to assess the safety of an oral food challenge (OFC) with cow's milk proteins and to assess the tolerance of cow's milk proteins in children with a food allergy after introducing cow's milk into the diet.

The aim of the study is to assess the safety of an oral food challenge test with cow's milk proteins and to assess the tolerance of cow's milk proteins in children with food allergies after introducing cow's milk into the diet.

The study covers children over 12 months of age diagnosed with cow's milk allergy, treated with a non-dairy elimination diet based on extensively-hydrolyzed formulas or amino acid formulas, admitted to the Department of Pediatrics, Gastroenterology and Nutrition to conduct an open oral food challenge. In all children, after appropriate assessment and qualification (interview, physical examination, skin prick tests, results of allergen - specific immunoglobulin E (IgE), total blood count, fecal calprotectin and lactoferrin), an oral food challenge test with cow's milk will be performed. The oral food challenge test will be carried out in accordance with current standards and with child protection in the event of an adverse reactions. During the food challenge test (first 24 hours), after 2 weeks (phone survey) and 3 months after the test (visit to the Department) the frequency, severity and type of allergic reactions and cow's milk protein tolerance will be assessed. The safety of oral food challenge with cow's milk protein in children previously fed with extensively - hydrolyzed formulas or amino acid formulas will be compared. The results of allergy tests, total blood count and intestinal inflammatory markers (fecal calprotectin and fecal lactoferrin) will also be assessed before and 12 weeks after oral food challenge. The assessment of the incidence and severity of allergic reactions and tolerance of cow's milk proteins after introduction into the diet in children challenged with cow's milk proteins may help to establish guidelines on the qualifications and how to conduct an oral challenge test.

Inclusion Criteria:

• children aged from 13 months to 15 years
• children diagnosed with cow's milk allergy treated with a dairy-free diet
• informed consent of the child's parents/legal guardians to participate in the study

Exclusion Criteria:

• occurrence of anaphylactic reaction after ingestion cow's milk proteins less than 12 months
• positive skin prick test with cow's milk proteins
• milk specific serum IgE values > 17,5 kU/L
• age below 13 moths
• no consent of the child's parents/legal guardians to participate in the study