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LTP syndrome (lipid transfer protein cross-reactivity)

By Symon, Every Label ·

If you have had a whole-body reaction to peach, to several unrelated plant foods, or to a food you ate before exercise, the protein behind it may be one family called the lipid transfer proteins, or nsLTP. These are small, tough defense proteins that many plants carry in their skin and outer layers. The single most important thing to understand about them is what sets them apart from the protein behind the milder oral allergy syndrome: lipid transfer proteins are heat-stable and digestion-stable. Cooking does not break them down, and the stomach does not break them down. That is the whole reason an LTP reaction can be a serious, whole-body reaction rather than the itchy-mouth, raw-food-only pattern of oral allergy syndrome.

That stability has three practical consequences that run through this entire page. LTP reactions can be systemic, including anaphylaxis, not just local. They are often Mediterranean-dominant, much more common in southern Europe than in northern Europe or the US. And they are frequently cofactor-amplified, meaning exercise, anti-inflammatory painkillers (NSAIDs), or alcohol around the time of eating can turn a tolerated food into a reactive one. Peach, and its protein Pru p 3, is the prototype and the usual primary sensitizer, the food the rest of the cluster is measured against.

This is the mechanism hub. It explains the protein first, then groups the member foods by how strongly they actually travel with an LTP allergy, then sends you to each food’s own page and to your allergist. The framing that matters most, and the one that makes this page the mirror image of the oral allergy syndrome page, is this: a positive LTP test is a serious marker, not a reassuring one. Where a claim is a verified cross-reactivity fact, it is drawn from the project’s cross-reactivity floor. Nothing here clears any food for you to eat, and none of it replaces your allergist.

The molecular why: one tough protein, shared across many plant foods

The lipid transfer protein is the spine of this whole story, so it goes first.

Non-specific lipid transfer proteins (nsLTP, part of the plant prolamin family) are small defense proteins that plants make to protect their surfaces, so they concentrate in skins, peels, and outer layers. The prototype, and the reason this cluster carries the protein’s name, is Pru p 3, the major lipid transfer protein in peach. Many unrelated plant foods carry an nsLTP that is similar enough in shape to Pru p 3 that an immune system sensitized to one can react to the others. Because the foods are botanically unrelated (a fruit, a nut, a cereal grain, a legume), this is not a “tree nut allergy” or a “fruit allergy.” It is an allergy to a protein that turns up across plant categories, which is why this page is built around the protein rather than around any one food.

One pair of properties drives everything below, and it is the exact opposite of the protein behind oral allergy syndrome:

  • It is heat-stable and digestion-stable. Cooking, baking, roasting, and processing do not break the lipid transfer protein down, and it survives the stomach intact. So the reaction is not defused by cooking, and the allergen can be absorbed whole and act on the whole body rather than staying in the mouth. This is the mechanical reason an LTP reaction can be systemic.
  • It is one shared shape, so a peach LTP allergy can reach many foods at once. Because all of these foods carry a Pru p 3 lookalike, sensitization to the peach protein can light up apple, cherry, walnut, hazelnut, peanut, wheat, and more. How far it actually reaches is highly patient-specific: some people sensitized to Pru p 3 react to almost every lipid transfer protein food, some only to peach and a few tree nuts, and some only to peach. That variability is real, and it is exactly why no food in this cluster can be assumed safe without testing.

There is a third property that turns this from a broad allergy into a genuinely tricky one: cofactor amplification. Lipid transfer protein reactions are frequently triggered, or made far worse, by a cofactor present around the time of eating, classically exercise, NSAID painkillers (such as ibuprofen or aspirin), or alcohol. The same food, in the same person, can be tolerated on a quiet day and cause anaphylaxis when eaten before a run or with a painkiller. This is part of why an LTP allergy is hard to pin down by trial and error, and it is one more reason this is a test-and-plan-with-your-allergist condition, not a try-it-and-see one. The exercise-triggered version of this story (wheat-dependent and food-dependent exercise-induced reactions) has its own pages, linked below.

How this differs from oral allergy syndrome: the contrast that matters most

This is the single most important thing to get right, so it sits up front rather than in a footnote.

Two different plant proteins drive two very different patterns, and they are often confused because the same food can carry both.

  • PR-10 proteins are the ones behind oral allergy syndrome (also called pollen-food syndrome). They are fragile: heat-labile and digestion-labile. They fall apart with cooking and in the stomach, so the reaction usually stays in the mouth and throat, is usually to the raw food, and is usually mild. A positive PR-10 result fits that usually-local picture. (We cover that protein and that pattern in full on the oral allergy syndrome page.)
  • Lipid transfer proteins are the opposite. They are tough: heat-stable and digestion-stable. They survive cooking and the stomach, so the reaction can be whole-body, can happen to cooked and processed foods, and can be severe. A positive lipid transfer protein result is a red flag, not a reassuring one.

So the two results mean almost opposite things. This is why telling them apart by component testing is not a technicality, it is the difference between “usually local and usually mild” and “potentially systemic.” And it is why the same food can be safe-feeling for one person and dangerous for another: apple carries both Mal d 1 (the fragile PR-10) and Mal d 3 (the tough lipid transfer protein); peach carries Pru p 1 (PR-10) and Pru p 3 (LTP); peanut carries Ara h 8 (PR-10) and Ara h 9 (LTP); hazelnut carries Cor a 1 (PR-10) and Cor a 8 (LTP). A bare “I tested positive to peach” or “to peanut” tells you nothing until you know which protein your antibodies are aimed at.

The practical rule: if your reactions are systemic, happen to cooked food, or happen around exercise or painkillers, the lipid transfer protein is the protein to ask your allergist about, and a positive lipid transfer protein test is treated as a serious marker, not as the reassuring “it is just oral allergy syndrome” result. This page does not convert any lipid transfer protein result into a clearance to eat the food.

The member foods, grouped by how strongly they travel with an LTP allergy

This is the map of the cluster: the foods whose lipid transfer protein cross-reacts with peach Pru p 3, sorted by how reliably an LTP allergy reaches them. A reminder before the list: the verified cross-reactivity floor for this cluster has not yet cleared any of these individual food edges, so each one below is described as the documented lipid transfer protein pattern, not as a settled per-food rule, and each one routes to component testing and your allergist rather than to a yes-or-no answer here. Because the reach is patient-specific, a positive test across many of these foods is common and does not by itself tell you which ones will actually cause a reaction.

Peach is the anchor of the whole cluster.

  • Peach (Pru p 3). Peach lipid transfer protein is the prototype and the standard diagnostic marker for the whole syndrome, and peach is the most common primary sensitizer. The allergen concentrates in the fuzzy skin, so the skin is more allergenic than the flesh. Peach reactions in this syndrome can be systemic, not the mild oral pattern.
  • Apple (Mal d 3), cherry (Pru av 3), apricot (Pru ar 3), and the other stone fruits and pomes. These Rosaceae fruits carry lipid transfer proteins closely related to peach Pru p 3 and are the foods most often reported alongside peach in this syndrome. The same heat-stability applies, so a cooked or processed version (juice, compote, baked fruit) is not reliably safe.
  • Grape (Vit v 1) and kiwi (Act d 10). Both carry lipid transfer proteins and are part of the same cluster.

What to do with that: an LTP-sensitized person who reacts to peach commonly tests positive across this fruit group and may or may not react to each one. Whether any specific fruit is safe for you, raw or cooked, is a component-testing and allergist question, not a rule. This page does not clear any of them, and because the protein is heat-stable, “just eat it cooked” is not the answer it is for oral allergy syndrome.

The tree nuts and peanut: where the lipid transfer protein crosses into the nut and legume world

The lipid transfer protein reaches well beyond fruit, which is what makes this a cross-category syndrome rather than a fruit allergy.

  • Walnut (Jug r 3), hazelnut (Cor a 8), and almond (Pru du 3). Each of these carries a lipid transfer protein in the peach Pru p 3 family. These are heat- and digestion-stable, so a positive result to one of them is a serious marker, not a reassuring “minor” one, and roasting or baking the nut does not make it safe.
  • Peanut (Ara h 9). Peanut’s lipid transfer protein, Ara h 9, is the marker behind the Mediterranean peanut-allergy phenotype, where lipid transfer protein sensitization, rather than the storage proteins seen elsewhere, drives the reaction, and it is capable of systemic reactions amplified by cofactors.

A crucial caution sits underneath this group. These same nuts and peanut also carry heat-stable storage proteins (the 2S albumins, 7S vicilins, and 11S legumins), which are a separate serious marker, and a positive test to one of those is likewise a red flag for whole-body reactions, not a reassuring low-risk result; these are heat-stable and survive digestion, so cooking does not make the nut safe. Hazelnut and walnut in particular commonly cause dual allergy through their shared storage proteins. The point for this page is that with nuts and peanut, both the lipid transfer protein and the storage proteins are heat-stable serious markers, so a positive result to any of them is treated as serious. The full storage-protein story lives on the seed and tree-nut storage protein cluster, the other heat-stable serious-marker cluster.

What to do with that: a positive nut or peanut test in a lipid-transfer-protein-sensitized person is a serious marker that needs component testing to characterize and an allergist to manage. This page does not clear any nut or peanut for you.

Wheat and the other plant foods: maize, mugwort, and plane tree

The lipid transfer protein appears in cereals and in pollens too, which is part of why this syndrome can be confusing on a test.

  • Wheat (Tri a 14). Wheat carries a lipid transfer protein, Tri a 14. Wheat lipid transfer protein reactions are closely tied to the cofactor story, exercise-dependent and NSAID-amplified reactions in particular, which is covered on the exercise-induced reaction pages linked below rather than restated here.
  • Maize (Zea m 14). Maize (corn) carries the lipid transfer protein Zea m 14, which is heat-stable, so a maize reaction in this syndrome is not abolished by cooking.
  • Mugwort (Art v 3) and plane tree (Pla a 3). These pollens carry lipid transfer proteins in the same family. Mugwort lipid transfer protein in particular is a known sensitizer that links pollen exposure to lipid transfer protein food reactions in some people.

What to do with that: as with the rest of the cluster, a positive result here is a serious marker to characterize with component testing and an allergist, not a per-food rule you can read off this page.

The serious-marker spine: why a positive LTP test is a red flag, not a reassurance

This is the safety backbone of the page, and it is where the contrast with oral allergy syndrome has its hard edge.

Lipid transfer proteins belong to the small group of heat-stable, digestion-stable plant allergens (alongside the seed storage proteins) that do not follow the fragile-PR-10 rule. Because they survive cooking and digestion, a reaction driven by them can be whole-body rather than confined to the mouth. That is why a positive lipid transfer protein test, or a positive storage-protein test, is read as a red flag for systemic reactions, not as a reassuring low-risk result; these proteins are heat-stable and survive digestion, so roasting, baking, or cooking does not make the food safe.

The heat-stability is not abstract. It is the same reason a thoroughly cooked food can still trigger a reaction in other heat-stable allergens: for example, lentil allergens are heat-stable, so even well-cooked lentils can still cause reactions. Apply that same logic to every lipid transfer protein food: the cooked, baked, juiced, or processed version is not reliably safer, which is the opposite of the cooking-helps pattern of oral allergy syndrome.

Two more things make a lipid transfer protein result something to take seriously rather than shrug off. First, the reactions are frequently cofactor-amplified: a food that seems tolerated can cause a systemic reaction when eaten around exercise, NSAID painkillers, or alcohol, so “I have eaten it before and was fine” does not establish that it is safe. Second, concentrated, large-dose forms of a protein are a higher-risk exposure than trace forms (for example, textured or hydrolyzed soy protein is a concentrated, higher-risk soy ingredient, not the trace class), which matters because a large protein dose is one of the things that can tip a cofactor-amplified reaction over the edge.

So the rule this whole page rests on: a positive lipid transfer protein test is a serious marker. It is not a clearance, it is not “just oral allergy syndrome,” and cooking does not undo it. What it actually means for the specific foods you can and cannot eat is a component-testing and allergist question, and managing the cofactors is part of the plan.

What is NOT this syndrome: the boundaries worth drawing

The lipid transfer protein cluster is broad, but it has edges, and drawing them keeps the picture honest. None of these boundaries is a clearance to eat a food.

A positive PR-10 test is not a lipid transfer protein result, and the two mean almost opposite things. This is the central distinction, repeated here because it is the one that changes management. A result driven by the fragile PR-10 component fits the usually-local oral allergy syndrome picture; a result driven by the heat-stable lipid transfer protein is a red flag for whole-body reactions and is not reassuring. The same food can carry both. If your reactions are systemic, happen to cooked food, or happen around exercise, the lipid transfer protein is the one to ask about. The mild PR-10 / oral allergy syndrome side has its own page.

Celery is a known exception in the related vegetable cluster, and it does not follow a mild pattern. In pollen-sensitized people, especially those sensitized to mugwort, celery can cause systemic reactions, including anaphylaxis, driven by heat-stable proteins (a lipid transfer protein and a defensin) rather than by the fragile PR-10. So celery should be treated as a possible systemic reactor, not folded into any mild-mouth-only group, and confirmed with your allergist rather than assumed low-risk. The deeper celery and spice mechanism lives on the mugwort, celery, and spice page.

This is not a clearance for the cooked food. With oral allergy syndrome, cooking often helps because the protein is fragile. With lipid transfer proteins, that logic does not hold: the protein is heat-stable, so cooked, baked, and processed foods are not reliably safe. The cleared verification floor for this site has not signed off any “safe to eat” claim for these foods, raw or cooked, so this page does not give you one. Whether you can eat a specific lipid transfer protein food is a component-testing and supervised-challenge question for your allergist, and it has to account for the cofactors.

Where studies disagree

Two genuinely unsettled areas are worth seeing as disagreements rather than settled facts.

Co-sensitization versus real reactions, and how far the cluster reaches in any one person. A lipid-transfer-protein-sensitized person, especially one who is Pru p 3 positive, very commonly tests positive across a long list of plant foods, but how many of those foods actually cause a reaction varies enormously: some people react to nearly all of them, some only to peach and a few nuts, some only to peach. The test and the clinical reaction are measuring two different things, and for this cluster the gap is wide and patient-specific. That gap is exactly why a broad positive lipid transfer protein panel is not an instruction to avoid every food on it, and equally why it is not permission to eat them, and why component testing plus a careful history, not the panel alone, is what decides. The difference from oral allergy syndrome is that the floor of severity is higher here, so the cost of guessing wrong is greater.

How big a role cofactors play, and how to manage them. It is well documented that lipid transfer protein reactions are often cofactor-amplified by exercise, NSAIDs, or alcohol, but how reliably, in whom, and with which foods is not settled, and the same food can behave differently on different days depending on the cofactor. The practical consequence is conservative: a food that seemed tolerated cannot be assumed safe, because the next exposure may coincide with a cofactor, which is why the management is built around component testing and an allergist-guided plan rather than around past tolerance. The exercise-dependent reactions, where this cofactor story is most developed, are covered on the exercise-induced reaction pages.

Testing and confirmation

Cross-reactivity questions in this cluster are answered the same way as the core diagnosis: component-resolved testing, and where needed a supervised challenge with cofactor awareness.

A standard whole-extract blood test or skin prick to a food tells you the immune system has noticed it, but for this cluster it cannot tell a fragile PR-10 result from a heat-stable lipid transfer protein result, and that distinction is the whole game. Component testing breaks the result down to the actual proteins. For a lipid-transfer-protein-sensitized person, the key marker is peach Pru p 3 (the prototype the syndrome is defined against), read alongside the lipid transfer proteins of the other suspect foods (for example walnut Jug r 3, hazelnut Cor a 8, peanut Ara h 9, wheat Tri a 14) and against the PR-10 components, so the heat-stable serious markers are told apart from the fragile oral-only ones. That distinction decides whether a positive food result reflects the mild pattern or the dangerous one, and it changes the management completely.

Where component testing and history still disagree, a supervised oral food challenge is the test that settles whether a specific food can actually be eaten, but for this syndrome the challenge has to account for the cofactors: a food tolerated at rest in the clinic may still react with exercise or a painkiller, so the plan an allergist builds includes when and how the food is eaten, not just whether. It is done with your allergist, never at home, and nothing on this page is that clearance.

The members (each food’s own page):

The neighboring hubs:

  • Oral allergy syndrome (PR-10 / birch): the milder, fragile-protein syndrome this page is the mirror image of (why raw fruit itches but the cooked version often does not, and why that is the opposite of the lipid transfer protein story)
  • Seed and tree-nut storage proteins: the other heat-stable serious-marker cluster (the storage proteins that, like lipid transfer proteins, survive cooking)
  • Wheat-dependent exercise-induced anaphylaxis (WDEIA), and food-dependent exercise-induced reactions (forthcoming): where the cofactor and exercise story lives in full
  • Mugwort, celery, and spice (pollen-food): where the celery and spice mechanism lives in full (forthcoming)
  • Latex-fruit syndrome: the related chitinase-driven plant-food cluster (forthcoming)
  • Tree nuts and legumes, and mustard: the family pages (the category, the label-scan and FALCPA detail)

Frequently asked questions

What is LTP syndrome, and how is it different from oral allergy syndrome?

LTP syndrome is an allergy to lipid transfer proteins, a family of tough plant proteins found across many unrelated plant foods (peach is the prototype). The key difference from oral allergy syndrome is the protein’s durability: lipid transfer proteins are heat-stable and digestion-stable, so they survive cooking and the stomach, which means an LTP reaction can be whole-body rather than the itchy-mouth, raw-food-only pattern of oral allergy syndrome. That also makes a positive LTP test a serious marker rather than a reassuring one, the reverse of a PR-10 / oral allergy syndrome result. This page explains the mechanism, but it does not tell you any food is safe to eat; that is a component-testing and allergist question.

I am allergic to peach. What other foods should I be tested for?

Peach (its protein Pru p 3) is the anchor of this cluster, and people sensitized to it commonly test positive across other Rosaceae fruits (apple, cherry, apricot), tree nuts (walnut, hazelnut, almond), peanut, and sometimes wheat, grape, kiwi, and maize. How far it reaches is very patient-specific: some react to almost all of them, some only to peach and a few nuts, some only to peach. Which foods actually matter for you is decided by component testing and your allergist, not by this list. This page does not clear any of those foods for you.

Can I eat these foods if they are cooked?

Not reliably, and this is the important difference from oral allergy syndrome. Lipid transfer proteins are heat-stable, so cooking, baking, and processing do not break them down, and a cooked or processed food can still cause a reaction. The “cooked is fine” rule that often applies to oral allergy syndrome does not apply here. This site does not publish a “safe cooked” claim for these foods, so whether you can eat a specific food in any form is a supervised question for your allergist.

Why did I react to a food only when I exercised, or after taking ibuprofen?

That is the cofactor pattern, and it is characteristic of lipid transfer protein reactions. Exercise, NSAID painkillers (such as ibuprofen or aspirin), and alcohol around the time of eating can turn a food you usually tolerate into one that causes a systemic reaction, so the same food can be fine on one day and dangerous on another. Because of this, having eaten a food safely before does not prove it is safe, and managing the cofactors is part of the plan your allergist builds. The exercise-triggered version of this has its own pages, linked above.

Is a positive LTP test good news or bad news?

It is a serious marker, not a reassuring one, which makes it the opposite of a PR-10 / oral allergy syndrome result. Because lipid transfer proteins are heat-stable and the reactions can be systemic and cofactor-amplified, a positive lipid transfer protein result is read as a red flag for whole-body reactions, not as a low-risk finding. What it means for the specific foods you can eat is a question for component testing and your allergist.

Why is LTP allergy talked about as a Mediterranean thing?

Lipid transfer protein sensitization is much more common in southern Europe and the Mediterranean than in northern Europe or the US, which is why it is described as Mediterranean-dominant and why, for example, the lipid transfer protein form of peanut allergy is more typical there than the storage-protein form seen elsewhere. It is not exclusively Mediterranean, and it can occur anywhere; the geography just changes how likely a given allergy is to be lipid-transfer-protein-driven. Component testing is what identifies it in any individual.

References and medical review

This page is pending independent medical review; the note at the top of the page applies until a reviewer is assigned. The verified serious-marker claims, that a positive heat-stable component test is a red flag rather than a reassurance, that hazelnut and walnut commonly cause dual allergy through shared heat-stable storage proteins, that heat-stable allergens survive cooking so a thoroughly cooked food can still react, and that concentrated, large-dose protein is the higher-risk form, resolve to the project’s conservative cross-reactivity floor, each carrying its own tier-1 source there. The lipid transfer protein membership map and the syndrome-level mechanism (the peach Pru p 3 prototype, the heat- and digestion-stability, the systemic severity, the Mediterranean-dominant phenotype, the cofactor amplification by exercise, NSAIDs, and alcohol, and the patient-specific reach across peach, apple, cherry, apricot, almond, kiwi, grape, walnut, hazelnut, peanut, wheat, maize, mugwort, and plane tree) resolve to the project’s cross-reactivity database, which is not yet signed off by a medical reviewer, and will carry author-year citations at that review. Figures not yet pinned to a stable source, such as the Mediterranean-prevalence percentages, the homology percentages, and the cofactor threshold numbers, are omitted rather than stated. No individual food edge in this cluster has been cleared on the verified floor, so each member food routes to component testing and your allergist rather than to a settled per-food rule here.

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