Oral Food Challenge for Babies: What to Expect on the Day

An oral food challenge is the test allergists turn to when skin-prick or blood results leave the answer unclear. The AAAAI describes it as a procedure "in which a food is eaten slowly, in gradually increasing amounts, under medical supervision, to accurately diagnose or rule out a true food allergy." A 2019 review by Calvani and colleagues in the journal Medicina calls it "the gold standard for diagnosis of a food allergy", because history and lab tests on their own "cannot make a certain diagnosis".

The pace is slow on purpose. The AAAAI says each serving usually comes 15-30 minutes after the last, with a check for symptoms before every one, until a meal-sized portion has gone in. Milton Keynes University Hospital gives the food at 20 minute intervals. For a supervised milk challenge, its leaflet suggests hiding the milk in something the child already drinks, for example "mixing cow's milk with soya milk", so the child eats the full amount.

The whole day is built around the chance of a reaction. The Milton Keynes leaflet says so plainly: "There is a potential risk that your child will have a reaction to the food they are being challenged to. This is why the food challenge is done in a hospital setting." A paediatric nurse watches the child throughout, "a doctor will always be available if needed", and the leaflet names the medicines on hand, from antihistamine for milder symptoms to adrenaline for a severe reaction.

Cambridge University Hospitals explains who tends to be booked in. Some children may well have outgrown an allergy "but they have had a severe reaction to the food in the past". Others have had tests that did not settle whether an allergy exists at all. Neither is something a parent could safely test on a Sunday afternoon with a yoghurt pot. Reintroducing milk at home, step by step, is a separate plan written by a dietitian for particular children, and our milk ladder explainer covers that one.

Most of the preparation is about medicines and timing. The Cambridge leaflet says the child "must stop taking antihistamines during the five days before a food challenge", naming Piriton and cetirizine among others, and warns that some cold remedies contain them too. Asthma inhalers, eczema creams and topical steroids carry on as normal. The AAAAI gives the reason: antihistamines "might mask mild early symptoms". It also tells families to ask their own doctor how long to stop the particular one they use, so the five days is Cambridge's rule and not a universal one.

Breakfast rules differ too. Cambridge asks for the usual breakfast, with a light snack allowed up to an hour before. The AAAAI says you may be told to avoid food or eat only a very light meal. A cough, cold, sickness or poorly controlled asthma means the challenge is rebooked, so Cambridge asks parents to phone ahead. On the day it suggests planning for four to five hours at the clinic, and for baked milk or egg challenges parents make a cake or biscuits at home and bring them in.

Reactions do happen, and the leaflets are calm about them. The AAAAI says most reactions during a challenge are skin or stomach symptoms, and they are "usually mild because the testing is done gradually with small amounts of food at the start, and feeding is stopped at the onset of symptoms." Antihistamine is the usual treatment, with adrenaline and other medicines kept for anything more severe.

A reaction makes for a longer stay. The AAAAI describes watching the child for at least two to four hours from the point symptoms settle, and the Milton Keynes leaflet adds that occasionally a child stays in hospital overnight. A reaction is also a result in its own right. In the Milton Keynes wording, a positive challenge means the child "is allergic and needs to strictly avoid that food", and the hospital writes to the GP with the outcome. Reading that, we found the day easier to picture: a clear answer, reached in a room set up to treat a bad reaction quickly.

A passed challenge comes with homework. Cambridge says that if the child eats the full portion with no reaction, "they must continue including this food in their diet at least three to four times per week". The AAAAI recommends starting regular meals of the food at home the following day, and adds that symptoms after a passed challenge are uncommon.

The Cambridge leaflet is firm enough about this that it asks parents who doubt they can keep the food going at home to get in touch before the challenge, to talk over whether it is still the right step. A partial pass has its own rule: if the child stops short of the full portion without reacting, the team decides on the day whether that smaller amount can continue at home. Cambridge also books a follow-up with the paediatric allergy dietitian six weeks later. After a supervised milk challenge, passing means milk becomes an ordinary part of the week, in amounts Cambridge says may grow over time with support from the allergy team.

The allergist will already have the history from clinic, and a written log makes that history quicker to check. Timing matters more than it first seems. The AAAAI notes that delayed allergies change how the test is run: with FPIES, symptoms usually start at least two hours after eating, and "the dosing and observation time for an OFC can be adjusted to address an individual patient's pattern of reaction."

A log for challenge day would show each past exposure to the food with the form it came in (milk in a sauce, yoghurt, baked into a muffin), roughly how much, and the time any symptom started, alongside dated photos taken in daylight. We would add the date and time of the last antihistamine dose, since the five-day rule counts back from it, and any cough or cold in the week before. The layout is the same one we describe in building a food diary for the paediatrician, and the milk allergy symptoms post explains the fast and slow patterns worth recording.