Comparison of Common Seed Allergens and Their Cross-Reactivity
| Seed | Officially named allergens | Protein family | Molecular weight (kDa) | Reported cross-reactivity | Notes |
|---|---|---|---|---|---|
| Sesame | Ses i 1, Ses i 2; Ses i 3; Ses i 6, Ses i 7; Ses i 4, Ses i 5 | 2S albumins; vicilin; 11S globulins; oleosins | 7–57 | Poppy seed, kiwi, hazelnut (reported); peanut and tree nuts mostly co-allergy | US major allergen since January 1, 2023; anaphylaxis is common |
| Sunflower | Hel a 15, Hel a 16, Hel a 17; Hel a 3 | 2S albumins; LTP | 10–15; 9 | Mugwort and other Asteraceae weed pollen | Anaphylaxis documented. Hel a 1 is a pollen (airway) allergen. |
| Mustard | Sin a 1; Sin a 2; Sin a 3; Sin a 4 | 2S albumin; 11S globulin; LTP; profilin | 14; 51; 12.3; 13–14 | Mugwort pollen; other Brassicaceae such as rapeseed | Anaphylaxis documented. Major allergen in the EU and Canada (not the US). |
| Pumpkin seed | Cuc ma 4; Cuc ma 5 | 11S globulin; 2S albumin | —; 14 | Limited data | Reactions reported. Melon Cuc m 2 is a different allergen (profilin). |
| Flax (linseed) | Lin u 1 | 2S albumin | 13 | Limited data | Severe reactions reported |
| Pine nut | Pin p 1 | 2S albumin | 6–15 | Often an isolated allergy | Reported reactions are frequently anaphylaxis |
| Chia | None officially named | — | — | Sesame and mint-family herbs (case reports) | Reactions reported |
Key Findings
- Sesame is the most common and most often severe seed allergy. Its main allergens are 2S albumins (Ses i 1, Ses i 2), with oleosins (Ses i 4, Ses i 5) retained in unrefined and toasted sesame oil. A link with poppy seed is documented.
- Sunflower seed allergy is uncommon but can be severe; anaphylaxis is documented. Its seed allergens are 2S albumins (Hel a 15–17) and an LTP (Hel a 3). It is associated with mugwort and other Asteraceae weed pollen, not grass pollen.
- Mustard can cause anaphylaxis. It is a major allergen that must be labeled in the EU and Canada (not the US), and it is associated with mugwort pollen and other Brassicaceae such as rapeseed.
- Pine nut allergy (Pin p 1, a 2S albumin) is often isolated, and many reported reactions are anaphylaxis.
- Pumpkin, flax and chia allergies are less common, with limited data; chia has no officially named allergens.
- Molecular weight does not predict how severe an allergy is; protein family and individual sensitization matter more.
Cross-Reactivity Risk Assessment
| Seed | Main risk to know about | Advice |
|---|---|---|
| Sesame | Common, often severe; hidden in many foods | Avoid strictly if allergic; ask about poppy seed |
| Sunflower | Uncommon but can be severe; sunflower butter is often made on shared lines | Use only if tolerated and the brand controls cross-contact |
| Mustard | Can be severe; not a US major allergen, so it may appear only as "spices" | Ask manufacturers; check imported and EU/Canadian labels |
| Pumpkin, flax, chia | Less common; data limited | Introduce only with allergist advice if you have other seed allergies |
| Pine nut | Often isolated but frequently severe | Avoid unless an allergist confirms tolerance |
Clinical Implications for Seed Allergy Patients
- Anyone with a seed allergy should ask their allergist which other seeds are safe; tolerance is decided individually.
- Seed butters (sunflower, pumpkin) used as peanut or tree-nut substitutes are often made on shared lines — choose brands that control cross-contact.
- Mustard and many seeds are not US major allergens, so they may appear only as "spices" or "natural flavors" on US labels. Imported EU and Canadian foods must declare mustard.
- Unrefined and toasted seed oils (such as sesame oil) contain allergenic protein.
Anaphylaxis: act fast. After an exposure, any breathing symptom (wheeze, repeated cough, throat tightness, hoarse voice), fainting or dizziness, or symptoms in two or more body systems (for example hives plus vomiting) is anaphylaxis — even without hives.
- Give epinephrine right away (auto-injector or nasal spray). Do not wait to see if symptoms get better.
- Call 911, even if symptoms improve.
- Lie flat with legs raised (sit up if breathing is hard). Give a second dose after 5–15 minutes if there is no improvement.
Antihistamines and steroids do not treat anaphylaxis and must never delay epinephrine. Carry two doses and follow the written emergency action plan from your allergist.