Introducing Solid Foods to Babies for Allergy Prevention
IgE-mediated allergic reactions do not typically occur on the first exposure to an allergen.
Mechanism of IgE-Mediated Allergy (Type I Hypersensitivity)
1st Exposure: Sensitisation Phase
- The first exposure to an allergen does not cause an allergic reaction.
- Instead, it leads to immune sensitisation:
- Allergen is processed by antigen-presenting cells → activates Th2 cells.
- Th2 cytokines promote IgE production by B cells.
- Allergen-specific IgE binds to FcεRI receptors on mast cells and basophils, “arming” them.
- This phase is asymptomatic, but the body is now “primed.”
⏱️ Timeframe for sensitisation:
Can vary from days to weeks, depending on:
- Allergen dose/frequency
- Route of exposure (e.g. parenteral = faster)
- Host immune status
2nd Exposure (or later): Elicitation Phase
- On subsequent exposure, the allergen cross-links bound IgE on mast cells.
- This causes immediate degranulation → histamine, prostaglandins, leukotrienes released.
- Clinical signs appear within minutes to 1 hour: urticaria, angioedema, bronchospasm, anaphylaxis, etc.
How Long Does Sensitisation Last?
- Once sensitised, IgE remains bound to mast cells for weeks to months (half-life of FcεRI-bound IgE is ~2 weeks).
- Memory B cells can persist for years, so reactions can occur years after a single sensitising event.
Non-IgE-mediated allergies (for comparison)
- May involve T cells or other antibody classes (e.g. IgG4).
- Often present with delayed symptoms (hours to days).
- Examples: FPIES, allergic contact dermatitis, coeliac disease.
Desensitisation (Allergen Immunotherapy)
| Mode | Description | Duration |
|---|---|---|
| Oral/SLIT | Daily low-dose allergen (e.g. pollen, dust mite, peanut) | Several months to years |
| SCIT | Subcutaneous injection; increasing doses over time | 3–5 years typical |
| Drug desensitisation | Temporary tolerance to antibiotics or chemo (e.g. penicillin) | Rapid (over hours); lost if not maintained daily |
Key Points
1. Timing of Allergenic Food Introduction
- Recommendation: Introduce common allergenic foods by 12 months of age in an age-appropriate form.
- Rationale: Early introduction reduces the risk of developing food allergies, especially in high-risk infants (e.g. eczema, family history of atopy).
2. Common Allergenic Foods
Include the following foods from around 6 months of age:
- Egg (well-cooked)
- Peanut (smooth peanut butter/paste)
- Cow’s milk (dairy)
- Tree nuts (e.g. almond or cashew paste, not whole nuts)
- Soy
- Wheat
- Sesame
- Fish and other seafood
3. Method of Introduction
- One allergenic food per meal to allow identification of triggers.
- Start small: Begin with ¼ teaspoon mixed into usual foods.
- Monitoring: Introduce new foods in the morning and observe for reactions over 2 hours.
- Lip test: Optional; rub a small amount inside the lip (not on skin).
- Avoid skin smearing or rubbing as it may increase sensitisation risk.
4. Frequency and Ongoing Exposure
- Continue feeding tolerated allergenic foods at least twice per week.
- Consistent exposure is key to maintaining tolerance.
5. Texture and Choking Prevention
- Modify food textures to suit developmental stage:
- 6 months: Smooth purées
- 8–9 months: Lumpy or mashed foods, soft finger foods
- 12 months: Cut-up family foods
- Avoid hard foods (e.g. raw apple, carrot, whole nuts). Cook, mash, or grate appropriately.
- Always supervise feeding.
6. Nutritional Considerations
- Provide a variety of foods to ensure adequate intake of:
- Iron, zinc, calcium
- Protein and fat-soluble vitamins
- Include iron-rich foods from ~6 months (e.g. meat, fortified cereals).
7. Signs Baby Is Ready for Solids
- Good head/neck control
- Interest in food, opens mouth for spoon
- Reaches for food or mimics eating
8. Managing Reactions
- Mild reaction: Redness around mouth, mild rash → observe.
- Moderate reaction: Vomiting, hives, swelling → stop food, seek GP advice.
- Severe reaction (anaphylaxis):
- Signs: Difficult/noisy breathing, tongue/lip swelling, pale/floppy
- Call ambulance immediately
- Timeframe: Most IgE-mediated reactions occur within minutes to 2 hours.
9. Infants with Known or Suspected Food Allergy
- Confirm diagnosis with allergy testing if needed.
- Follow ASCIA Action Plan.
- For cow’s milk, wheat, or multiple allergies, consult a paediatric dietitian.
- If baked forms of milk/egg are tolerated, continue them to promote tolerance.
10. Family History of Allergy
- Do not delay allergen introduction even with strong family history.
- Implement household safety measures:
- Use high chair
- Clean hands/face/utensils
- Avoid shared meals with allergic siblings during new food trials
11. Fluids
- Primary drinks: Breast milk or formula until 12 months
- Water: Introduce from 8 months in a cup
- Avoid fruit juice or cow’s milk as a main drink before 12 months
Supporting Evidence
- Early and regular introduction of allergenic foods significantly reduces food allergy incidence (LEAP, EAT studies).
- Delayed introduction increases allergy risk, particularly for egg and peanut.
- Guidelines endorsed by ASCIA, NHMRC, and international allergy societies.
from https://www.allergy.org.au/patients/allergy-prevention/ascia-how-to-introduce-solid-foods-to-babies