Growing up with a nut allergy, there's a good chance you also spent your childhood as the kid with the inhaler, the kid with permanently inflamed skin, or the kid constantly being asked if you need a tissue. Sometimes all three. It’s easy for those with less awareness to categorise this as just being a sickly child, or even weak, but the explanation is far more logical. These conditions share an underlying biological mechanism, and understanding that connection changes how you think about all of them.
The 'atopic march'
The atopic march describes a natural progression of allergies from infancy through to adulthood. This typically begins with eczema as a baby, followed by food allergies as a toddler, then hay fever, and eventually asthma.
The word atopic simply means 'prone to allergic reactions'. It signifies a heightened or overactive immune system response to common environmental triggers. Atopic individuals often experience conditions like chronic itchy skin, rashes, or respiratory distress. It's the wider term for the family of conditions that includes eczema, food allergies, hay fever, and asthma. The 'march' part refers to the way these conditions tend to arrive in a roughly predictable order. Not everyone with an allergy follows this sequence, and having one condition doesn't guarantee you'll develop the others. But the fact that they cluster together in the same individuals, in broadly the same order, tells us something important about what's driving them.
Nut allergy immunology - mast cells, IgE, and histamine
The common thread running through these conditions is a type of immune response called 'IgE-mediated hypersensitivity'. IgE is a type of protein called an antibody. Antibodies help the immune system recognise potential threats in the body. In people without allergies, IgE plays a relatively small role. In people with allergies, the immune system makes too much IgE in response to things that aren't supposed to be a threat to health, also known as allergens, for example: peanut proteins, birch pollen, animal dander, dust mites.
Once IgE antibodies are produced to match a specific one of these allergens, they attach to things in the body called mast cells. Mast cells are the immune system's way of responding very quickly to a threat, and they are found throughout the body in skin, the lungs, and the gut. The next time that same allergen appears, mast cells recognise it immediately and release a lot of inflammatory chemicals, including histamine, in what’s called a cascade. It's this big release of chemicals that produces the symptoms in an allergic reaction: the hives, the sneezing, the airway constriction, and ultimately anaphylaxis. The same fundamental process including mast cells, IgE, and histamine, is the background for nut allergies, asthma, hay fever, and eczema.
The difference is where in the body this process is happening. Eczema is that reaction playing out in the skin. Hay fever is the same reaction in the nasal passages. Asthma is the reaction in the airways. One overactive immune system causing responses in different areas. This of the driver behind anaphylaxis too, which is slightly different as it’s not restricted to one area of the body.
Anaphylaxis - systemic allergic reaction
Anaphylaxis is different from eczema, hay fever, or asthma in this sense, because it is a systemic allergic reaction. This means the immune response is happening across multiple parts of the body at the same time rather than being limited to one area like the skin or airways. Instead of just causing a rash, or just affecting breathing, the same mast cell and histamine response can involve the skin, lungs, gut, heart and circulation together at the same time. This is much harder to fight.
That is why symptoms of anaphylaxis can include hives, swelling of the lips or throat, breathing difficulty, vomiting, dizziness or collapse. It is not a different immune mechanism from eczema or hay fever. It is the same IgE-mediated response happening more widely and more rapidly throughout the body. The difference is the scale of the allergic reaction.
Understanding this helps explain why nut allergies are taken particularly seriously compared with many other allergic conditions. They’re the most likely to cause anaphylaxis which affects breathing and blood pressure at the same time, making them potentially fatal.
Why eczema often develops first
Some people with eczema have a genetic mutation that changes a protein in the skin called filaggrin. This protein helps keep the outer layer of our skin protected, so that moisture stays in and unwanted things stay out. Without enough filaggrin, the skin barrier becomes permeable, losing moisture and allowing allergens in. This might be how early sensitisation to food allergens begins, and helps explain why having eczema as an infant is one of the strongest risk factors for developing food allergies later.
So, a baby with this mutation could have skin that allows allergen proteins to enter the body before they've actually eaten them. The immune system encounters peanut or tree nut proteins through a damaged skin surface and learns to treat them as threats, later developing into allergies. This theory, called the 'dual-allergen exposure hypothesis', has changed how allergy scientists think about early prevention. It's one of the reasons current guidance encourages early introduction of peanuts in infants that are likely to have atopic conditions. Controlled oral exposure before skin sensitisation can occur, appears to reduce the risk of allergies developing. The order of these conditions matter, and the skin is where a lot of it starts.
This is also a reason why these conditions can appear across families, and over different generations. There are many factors involved as the immune system is so complex, both genetic and environmental, but having conditions like eczema and asthma in the family increase the risk of children developing food allergies [1].
How common is it to have all these conditions?
Not everyone with a nut allergy has these conditions, but there’s strong evidence tying them together. One study found that more 80% of children with food allergies have a history of skin conditions in their first year of life [2]. Having a food allergy in early childhood, a nut allergy specifically, significantly increases the risk of developing asthma and allergic rhinitis in later childhood. These aren't small associations. They suggest that if a child has one atopic condition, the likelihood of developing another is more common than not. For many families this won't be surprising. The surprise is usually that no one has explained why.
Research has shown that only a minority of children follow the atopic march sequence in order. It’s a general pattern measured across lots of people, and won’t be the reality for every individual. It’s a prediction that can help with prevention for infants and children, but doesn’t mean every child with a nut allergy will develop more conditions or vice versa. Compared to just a couple of decades ago, this is promising for allergy families who may be able to get help from medical professionals that results in a less restricted childhood.
What this means practically
Understanding that nut allergies and these conditions are linked by biology can change how to think about managing them day to day. Poorly controlled asthma is a recognised risk factor for more severe anaphylaxis [3], which means asthma isn’t just another separate condition sitting alongside a nut allergy. It can influence how the body responds during an emergency. Seeing eczema, hay fever, asthma and nut allergy as related conditions of the same immune over-reaction can also make patterns easier to recognise. For example, worsening hay fever seasons sometimes coincide with worsening asthma symptoms. Skin flare-ups sometimes appear alongside food sensitivity changes. These connections are different parts of the same immune response becoming more active at different times.
It also explains why allergy specialists often ask about seemingly unrelated conditions during appointments. Questions about inhalers, skin treatments or seasonal symptoms help build a clearer picture of overall allergy risk rather than focusing on one trigger alone. For families with children, understanding the atopic march can help explain why clinicians sometimes monitor eczema closely in infancy or discuss early food introduction strategies.
Considering how nut allergies fit into the wider atopic picture can make the condition feel less random and more predictable. For many people, that knowledge makes it easier to understand risk, recognise patterns earlier, and have more informed conversations about long-term allergy management.
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