Food allergies are more common now than ever. In fact, around 250 million people across the world have at least one food allergy. But what causes food allergies to develop?

Food allergies happen when the body’s immune system stops seeing certain foods as safe. This can happen because of a mix of genetic and environmental factors and problems with the skin or gut lining. Learn more about the different causes of food allergies, risk factors, and if you can prevent a food allergy from developing.

What Is the Main Cause of Food Allergies?

Allergies occur when the body’s immune system reacts to a substance that’s harmless to most people. In the case of food allergies, the allergens are typically specific proteins found in foods. Instead of ignoring these proteins, the immune system treats them like harmful invaders and triggers an allergic reaction.

There are two main types of food allergies: immunoglobulin E (IgE)-mediated and non-IgE-mediated.

IgE-Mediated Allergies

IgE-mediated allergies happen when your body’s immune system thinks a certain food protein (allergen) is dangerous. To protect you, your body makes special fighters called immunoglobulin E antibodies. When these fighters spot the allergen again, they cause your body to release histamine, a chemical that leads to allergy symptoms like hives or wheezing. These reactions are called IgE-mediated allergies.

Most systemic allergic reactions — including symptoms like lightheadedness, low blood pressure, and even life-threatening anaphylaxis (a severe allergic reaction) — are caused by IgE antibodies. But these antibodies can also cause localized food allergy reactions. Oral allergy syndrome (OAS) refers to a reaction to a food allergen where symptoms are limited to the mouth.

Non-IgE-Mediated Allergies

Not all food allergies involve IgE antibodies. In non-IgE-mediated allergies, other parts of the immune system are responsible for the reaction. These allergies usually cause delayed symptoms that appear several hours after eating the food. Instead of affecting the whole body right away, they more often target the digestive system, leading to problems like nausea, vomiting, diarrhea, or poor weight gain in young children.

Unlike IgE-mediated reactions, these allergies don’t cause sudden anaphylaxis, but they can still seriously affect your health and quality of life.

Risk Factors for Food Allergies

Science is good at finding correlations between certain factors and diseases. However, it’s important to note that correlation doesn’t equal causation. In other words, just because a risk factor is linked to a disease, doesn’t prove that it causes the disease.

Though risk factors for food allergies have been identified, so far, none have been pinpointed as the main cause of food allergies.

Age

Age is a factor in the development of food allergies. Though it’s possible to develop a food allergy as an adult, most food allergies appear during childhood.

Infants are at a higher risk for allergies to cow’s milk, egg, soy and wheat. The good news is that children with these early onset allergies often outgrow them. In contrast, allergies to tree nuts, peanut, shellfish, and fish often present between 1.5 and 3 years old and aren’t as likely to go away.

It’s also common for shellfish allergy and oral allergy syndrome to develop after childhood. It’s estimated that 4.7 percent to 20 percent of people with OAS are diagnosed as children, while 13 percent to 58 percent develop the allergic condition as adults. One study found that having eczema (a chronic skin condition), nasal allergies, or wheezing at ages 5 or 9 was linked to a higher risk of OAS at 13 years old.

Inherited Risk Factors

Some factors that increase your risk of developing food allergies are out of your control. These inherited risk factors are passed down to you via genes from your parents.

Family History

Having a close relative with allergies, eczema, or asthma can increase your risk of developing food allergies. Likewise, if you have eczema, asthma, or other types of allergies, you may have a higher risk of food allergies. It’s estimated that 30 percent of children with moderate to severe eczema also have food allergies.

Female Sex and Ethnicity

According to a large study published in the Journal of Allergy and Clinical Immunology, women are affected by food allergies and food intolerances more often than men. The study found that 4.2 percent of females and 2.9 percent of males had food allergies or intolerances. The same study found that people of Asian descent were more likely to develop food allergies than people from other ethnic backgrounds.

Certain Genes

The filaggrin (FLG) gene helps to regulate the skin barrier. People with FLG mutations (changes) don’t have as protective a skin barrier. This means that allergens like food proteins may have the ability to enter the skin and trigger sensitivity.

The leading theory that explains the role of the skin barrier in the development of food allergies is called the “dual allergen exposure hypothesis.” This theory suggests that a baby’s immune system becomes sensitized to foods when they touch their skin. If babies with vulnerable skin are touched by people with food on their hands or mouths, the protein is absorbed into the baby’s skin. The immune system interprets the food proteins as dangerous invaders when they pass through the skin.

In contrast, if a baby is introduced to a food protein by eating, rather than through contact with impaired skin, it’s thought to promote immune tolerance.

Other genes may also play a role in food allergies. Certain interleukin (IL)-4 gene mutations can increase immune response and may lead to the creation of IgE antibodies. Meanwhile, human leukocyte antigen mutations may increase the risk of peanut allergies, specifically.

Environmental Factors

Certain factors in your environment or other external influences may also increase your risk of food allergies. These environmental factors may impact how well your immune system tolerates allergens.

Disruption of the Gut Microbiome

One theory suggests that food allergies are caused by a disruption to the balance of microorganisms in the gut — referred to as the gut microbiome. Research has linked issues with microbiome balance to reduced immune system regulation and increased risk of food allergies.

The modern Western lifestyle includes improved sanitation and less exposure to farm animals. The “hygiene hypothesis” suggests that this lack of exposure to bacteria that used to be common is suppressing the appropriate immune system development. This can then result in conditions where the immune system becomes overactive, such as food allergies.

Being Born via Cesarean Section

One factor that may affect an infant’s microbiome is how they’re born. When babies are born vaginally, they often encounter vaginal and fecal microorganisms. However, babies born via cesarean section (C-section) aren’t exposed to these.

Compared to infants delivered vaginally, babies born via C-section tend to have lower volumes of Bacteroides and higher volumes of Firmicutes in their gut, both of which have been linked to food allergy. One study found that infants born via C-section were three times as likely to develop food allergies than those born vaginally.

Certain Early Exposures

In utero exposures (those occurring during pregnancy) such as smoking, limited nutrition, and obesity have been linked to a higher risk of allergic conditions in children.

Other early-life exposures may also disrupt the gut microbiome. Factors that can affect a baby’s microbiome — and may increase the risk of food allergies — include exposure to baby formula, antibiotics, and certain chemicals, such as food additives.

Low Vitamin D Levels

Another theory suggests that vitamin D levels may impact food allergy risk. Vitamin D is a nutrient the body makes when skin is exposed to sunlight. Research has shown that food allergies are more common in children who:

• Are born in fall or winter months
• Live far from the equator
• Are deficient in vitamin D

Health experts think food allergies affect these children more because vitamin D helps to regulate the immune system. However, it’s important to note that vitamin D supplements haven’t proven effective in preventing food allergies.

Can Food Allergies Be Prevented?

It may be possible to prevent some food allergies. In 2017, the National Institute of Allergy and Infectious Diseases (NIAID) released new guidelines on preventing peanut allergy. This guideline was based on the LEAP trial, which found that exposure to peanuts before age 1 resulted in an 80 percent reduction in peanut allergies at age 5 compared to peanut avoidance.

A follow-up study found that 4.4 percent of early exposure children had a peanut allergy at 12 years or older compared to 15.4 percent of those who avoided the nut.

Early introduction to eggs and milk may also help prevent food allergies. It might also be possible to prevent severe milk and egg allergies in children with mild reactions. Studies have shown that children with these allergies who could tolerate them in baked form could become tolerant of the food allergens. By consuming baked milk and egg each day, the children built up a tolerance to the food allergen. Food challenges showed that the children eating baked milk and egg were six and five times more likely to become tolerant than the children who avoided them.

Since the development of food allergies is so complex, there’s no certain way to avoid them. If you’re concerned that you or your child may have a high risk of developing food allergies, talk to your healthcare provider. Your child’s doctor may suggest early exposure to common food allergens. For adults, certain blends of probiotics may offer a way to balance the microbiome.

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On MyFoodAllergyTeam, people share their experiences with food allergies, get advice, and find support from others who understand.

Which of these causes or risk factors may have impacted your development of food allergies? Let others know in the comments below.