A peanut allergy is an immune system response that mistakenly identifies peanut proteins as harmful. This reaction involves Immunoglobulin E (IgE) antibodies, which trigger the release of chemicals like histamine, causing allergic symptoms. Peanut allergy is one of the most common food allergies in children, affecting an estimated two percent of children in the United States. Understanding the reaction timeline and recognizing the signs are important steps for parents introducing this food to infants.
The Reaction Timeline: Immediate vs. Delayed Onset
The vast majority of IgE-mediated food allergies, which account for the typical peanut allergy, manifest very quickly after ingestion. Symptoms often begin within minutes of the child eating the peanut-containing food, usually peaking within 30 minutes. Nearly all reactions appear within a two-hour window of exposure.
It is rare for an IgE-mediated reaction to occur significantly later than two hours. Reactions appearing four to six hours after eating are typically associated with different, non-IgE mediated immune responses, such as Food Protein-Induced Enterocolitis Syndrome (FPIES). Since the most serious reactions are rapid, parents should monitor their baby closely for at least two hours after the first peanut exposure.
Recognizing the Signs of an Allergic Reaction
An allergic reaction can affect multiple body systems, and signs may appear mild but can progress rapidly. The skin is often the first area to show symptoms, including hives (raised, red, itchy welts), or general flushing and redness. Swelling of the skin tissues, particularly around the lips, eyes, and face, can also occur.
The gastrointestinal tract frequently reacts, causing symptoms such as repeated vomiting, diarrhea, or severe abdominal pain and cramping. In infants, stomach distress may be indicated by arching the back or inconsolable crying. Neurologic or behavioral changes, such as sudden irritability, dizziness, or becoming pale and floppy, are also important signs.
Respiratory symptoms are concerning because they can signal anaphylaxis, a severe reaction. These signs include wheezing, a repetitive cough, a hoarse voice, or difficulty breathing. Swelling or tightness in the throat can also occur, manifesting as a change in the baby’s cry or noisy breathing.
Immediate Action Plan and When to Seek Emergency Care
When a reaction is suspected, parents must act quickly, as a mild initial reaction does not guarantee a mild overall course. For mild symptoms affecting only one body system, such as scattered hives or mild itchiness, an age and weight-appropriate dose of a non-drowsy antihistamine may be given, if approved by a physician. The child should be watched closely for any worsening of symptoms over the next several hours.
A severe reaction, or anaphylaxis, requires immediate administration of epinephrine, the first-line treatment. Epinephrine must be used immediately if the reaction involves trouble breathing, swelling of the tongue or throat, or symptoms in two or more body systems (e.g., hives combined with vomiting). After administering the auto-injector, 911 must be called immediately, even if the child appears to be recovering.
The child needs to be transported to an emergency department for observation, even if epinephrine resolves all symptoms. This is necessary due to the risk of a biphasic reaction, where symptoms temporarily resolve only to return hours later without further allergen exposure. A secondary reaction typically occurs within six hours of the initial episode and can be just as severe.
Safe Introduction Guidelines for Infants
Current medical guidelines recommend that most infants begin consuming peanut-containing foods to prevent the development of a peanut allergy. The Learning Early About Peanut (LEAP) study demonstrated that early, regular consumption significantly reduced the risk of allergy, particularly in at-risk infants. For infants without eczema or any food allergy, introduction can begin around six months of age, following successful feeding of other solid foods.
Infants considered at high risk (those with severe eczema, an existing egg allergy, or both) should have peanuts introduced as early as four to six months of age. These infants should first be evaluated by an allergist or pediatrician, as they may require allergy testing before introduction. The allergist may recommend the first feeding be done in the specialist’s office to ensure safety.
Peanut must be introduced in an age-appropriate form to avoid a choking hazard; whole peanuts or thick peanut butter should never be given. Safe options include mixing two teaspoons of smooth peanut butter into a fruit or vegetable puree, or using commercial peanut puff snacks that dissolve easily. For the protective effect to continue, the child should consume a total of six to seven grams of peanut protein, spread over three or more feedings per week.