There are multiple factors that contribute to a baby’s likelihood of developing food allergies. There’s no one specific thing that causes egg allergies. Most often, egg allergies are caused by a combination of genetics, eczema, avoiding eggs.
Family History of Egg Allergies
There is some genetic or family component to egg allergies. A baby has an increased risk of developing a food allergy if a parent or sibling has a food allergy, though it’s not a huge difference. The overall rate of egg allergy is 3% and in families with a history of egg allergy it might be closer to 6% or 10%.
No one has found a genetic marker for egg allergies. Family impact may have to do with epigenetics, or certain gut microbiome bacteria that are transferred from mother to child.
Having Eczema, and the Severity of the Eczema
Babies with eczema (also called atopic dermatitis or AD) have a compromised skin barrier. This condition is the single biggest predictor of food allergies, and there is also a known relationship between the severity of the AD and chance of sensitization to food.
Babies with AD have skin that feels rough to the touch because it is missing proteins like filaggrin that give skin its soft springy feeling. Why is a skin condition linked to food allergies? The short answer is that when the skin barrier is compromised, teeny bits of egg left on people’s hands, the table, or the ground break through the skin. Your baby’s body flags this skin-invader as a threat (sensitization). Later, when your baby eats eggs, the body ATTACKS.
That is why the LEAP study (the most important study on how to prevent food allergies) used babies with eczema as their definition of a high risk group, and why the current FDA language advises you to talk to your doctor before introducing allergens if your baby has eczema.
How Common Are Egg Allergies?
Babies are more likely than adults to suffer from egg allergies, and eggs are the second most common food allergy in children, behind cow’s milk. In the United States, 3% percent of babies are allergic to eggs.
But before you think “what’s going on in America??” know that egg allergies are way more common in Australia. Raw egg allergy was estimated to affect approximately 8.9% of 1 year old children in Australia (!) however many of these children can tolerate baked egg in their diets.
In contrast, peanut allergies affect 2% of the population.
When Do Egg Allergies Develop?
Almost all childhood food allergies develop before age 1. Of course, if parents avoid a food until their baby is 3 years old, they won’t notice the allergy until much later.
There are a few important points in the two sentences above:
Babies aren’t born with an egg allergy.
Food allergies don’t magically occur, they “develop.” When the body is first exposed to egg, it flags it as a threat, and then reacts to it at a later date.
There can be a big difference between when the egg allergy develops, and when parents notice the egg allergy. A baby exposed to egg on their skin could develop an allergy at 6 months old, but parents might think their baby got the allergy much later, when they first fed their baby eggs.
So when do egg allergies actually develop?
Infants have been known to develop an egg allergy as young as one month old, but more commonly, egg allergies develop between 6 months and 1 year. The highest levels of IgE antibodies for egg proteins were found in children around the age of 1, meaning that seems to be the peak age to develop a food allergy.
Why do egg allergies, and all food allergies, seem to develop between 6 and 12 months?
Infants’ immune systems get stronger and change rapidly in the second 6 months of life. Remember that a food allergy is a mistake the immune system makes. But to make that mistake, the baby has to have a strong, working immune system. Your baby doesn’t have the ability to develop an egg allergy until a bit later.
That is why parents should start working to prevent an egg allergy by 6 months old.
A Last Thought on the Timing of Food Allergies
Egg allergies are often “caught” before peanut allergies. It’s not clear if egg allergies actually develop first, or if people notice them first because it's easier to feed your baby very soft, finely chopped scrambled egg instead of peanuts. Either way, an egg allergy at 4 months old is considered a strong risk factor for developing a peanut allergy.