Tolerance Results and Immune Mechanisms in Cow´s Milk and/or Hen´s Egg Allergic Children Following Natural Evolution or Oral Immunotherapy

Inclusion Criteria: NAT-cohort: * Cow´s Milk and/or Hen´s Egg allergic patients 4 to 10 years old * sIgE levels to milk OR egg extracts between 0.35 to 35kUA/L * Positive entry Open food challenge with milk/egg with oFASS5 classification ≥2 with a maximum cumulative dose of up to 4193.7 mg of milk protein or 3110.8 mg of egg white protein * Having a mild to moderate food allergy severity per the Definition of Food Allergy Severity (DEFASE) score (\<13 points) * Having signed the informed consent OIT-cohort: * Patients in the compITO study (NCT06976775) who are undergoing OIT and have achieved full desensitization to the food by month 7 of the study (end of study) * Patients in the compITO study who are undergoing OIT and have achieved partial desensitization (tolerating a dose lower than the total dose, and a minimum of 3 doses above the entry challenge threshold) to the food by month 7 of the study (end of study) * Having signed the informed consent Exclusion Criteria: NAT-cohort: * Positive reaction in the entry open oral food challenge with a baseline Eliciting Dose (ED) 20 below the target ED20 for food. For milk, 23.1 mg (35.7 mg cumulative) of protein, or for egg, 19.5 mg (29.4 mg cumulative) of protein. * Patient desire or medical indication to initiate OIT at any time within 29 months of study entry. * No allergic reaction greater than oFASS5 grade 1 in the baseline challenge for the maximum cumulative programmed doses of 4193.7 mg of milk protein, or 3110.8 mg of egg white protein. * Immunological diseases, immunomodulatory/blocking therapies. * Severe atopic dermatitis according to the SCORing Atopic Dermatitis (SCORAD) classification * Severe allergy, according to a DEFASE score ≥13 * Spirometry values with moderate-to-severe airflow obstruction (FEV1 \<70%) * Poorly controlled asthma according to clinical criteria * Previous OIT for another food * Within the first 3 months of treatment with Subcutaneous Aeroallergen Immunotherapy * Within the first week of treatment with Sublingual Aeroallergen Immunotherapy * Presence or suspicion of Eosinophilic Esophagitis * Non-IgE-mediated allergy to milk or egg * Pregnancy * Significant medical comorbidities (renal, hepatic, or cardiac insufficiency, active infectious diseases, previous or concurrent cancers) * Inability to provide informed consent * Communication or cognitive barriers that prevent adherence to the protocol OIT-cohort: * Patients enrolled in the compITO study who have failed or withdrawn from the study for any reason. * Patients with uncontrolled Atopic Dermatitis or Asthma at the time of enrolment, or who have developed Eosinophilic Esophagitis. * Patients with confirmed pregnancy at the time of enrolment. * Patients who have developed significant medical comorbidities (renal, hepatic, or cardiac insufficiency, active infectious diseases, previous or concurrent cancers) at the time of enrolment. * Inability to provide informed consent. * Communication or cognitive barriers that prevent adherence to the protocol.