Food allergy affects 1 in 30 children, and is the commonest trigger for life-threatening reactions (anaphylaxis) in this age group. It is a major public health issue, with practical implications for industry, education and healthcare systems. Oral immunotherapy (OIT) is an emerging treatment option, where small, increasing doses of a food allergen are used to cause desensitisation, so food-allergic individuals no longer have symptoms when exposed to the trigger food. However, frequent allergic reactions during OIT (including anaphylaxis) are common, and can lead to patients having to stop treatment. In addition, food-allergic children usually dislike the taste of the food they are allergic too, which affects compliance and treatment success. There is a lack of longer-term data to inform cost-effectiveness analyses for OIT. The NATASHA study will recruit young people from age 6+ years with IgE-mediated peanut allergy, and young people aged 3+ years with IgE-mediated allergy to cow's milk, who will undergo oral immunotherapy for these allergens using real-world foods (taken carefully according to a standardised protocol under medical supervision). In addition to assessing efficacy and safety outcomes, we will also collect longer-term data to evaluate cost-effectiveness in the UK setting.