The investigators will conduct low-dose intranasal allergen challenges on children and young people with an indeterminate diagnosis of food allergy to cow's milk or peanut. Blood samples will also be taken, for conventional blood allergy diagnostics (allergy-specific Immunoglobulin E) and mast cell activation test (MAT). The data will be used to determine the diagnostic accuracy of two complementary, novel approaches to diagnose food allergy, in a representative clinical cohort.

Inclusion Criteria:

• IgE-sensitisation to peanut, (hen's) egg or cow's milk, with indeterminate clinical (allergy) status, defined as IgE-sensitisation below 95% positive predictive value (PPV) for diagnosis for either allergen-specific IgE or SPT, using published cut-offs OR clinician suspicion of tolerance (on basis of clinical history) despite IgE sensitisation >95% PPV cut-offs.
• Written informed consent from parent/guardian, with assent from children aged 6 years and above wherever possible. Participants aged over 16 years will need to provide their own informed consent.

Exclusion Criteria:

• Acute illness or current unstable asthma, defined as:

  1. Febrile ≥38.0oC in last 72 hours
  2. Acute wheeze in last 72 hours requiring treatment
  3. Recent admission to hospital in preceding 2 weeks for acute asthma

• Current medication

  1. Asthma reliever medication required in preceding 72 hours
  2. Recent administration of a medicine containing antihistamine within the last 3 days
  3. Current oral steroid for asthma exacerbation or course completed within last 2 weeks

• Unwilling or unable to fulfil study requirements

Anonymised data may be shared upon request to the Chief Investigator.