Birch Pollen Allergy: The PR-10 Allergen Behind Spring Rhinitis and Oral Allergy Syndrome

Birch pollen season typically runs from late March through May in most of the United States, with timing varying by latitude and elevation. Southern and coastal areas (e.g., Virginia, Oregon coast) may see pollen as early as mid-March, while northern New England, the Upper Midwest, and the Rockies may not peak until late April or early May. The season lasts roughly 4 to 8 weeks, with peak release occurring during warm, dry, and windy days. Tracking your local National Allergy Bureau (NAB) station data gives the most accurate day-by-day picture of when to expect the highest exposure.

This is oral allergy syndrome (OAS) caused by birch cross-reactivity. Your immune system produces IgE antibodies against Bet v 1 — the major birch allergen — and those same antibodies cross-react with Mal d 1, the structurally similar PR-10 protein in raw apple flesh and skin. The reaction occurs whenever you eat raw apple, year-round, regardless of whether birch is currently pollinating. Both Bet v 1 and Mal d 1 are heat-labile, so cooked applesauce, apple pie, and canned apples are usually safe. If your reactions progress beyond mouth tingling to throat tightening or hives, discuss epinephrine with your allergist.

As of June 2026, there is no FDA-approved sublingual immunotherapy tablet specifically for birch pollen in the United States. The Itulazax 12 SQ-Bet SLIT tablet is approved in more than 22 European countries and in Canada, but the manufacturer has not pursued a US FDA submission. US patients can access birch SLIT through providers who formulate custom under-the-tongue drops using standard SCIT birch extract — this is off-label use of an approved extract, supported by the European clinical evidence base. The Grastek and Oralair SLIT tablets (for grass pollen) are FDA-approved but do not cover birch.

In most cases, no. The PR-10 protein Mal d 1, which is the cross-reactive partner of Bet v 1 in apple, is heat-labile — it denatures rapidly when exposed to temperatures used in cooking, baking, canning, or pasteurizing. Patients with classic Bet v 1-driven OAS typically tolerate applesauce, baked apple, apple pie, and most commercial apple juices without triggering mouth symptoms. However, patients who also have elevated Bet v 2 (profilin) or who are sensitized to Mal d 3 (apple LTP) may react to cooked apple as well, because profilins and LTPs are more heat-stable. Component testing can identify which protein pattern you have.

Yes, research published by Anderegg et al. (2021) in PNAS found that North American pollen seasons have lengthened by approximately 8 days and pollen loads have increased by roughly 21 percent since 1990, with tree pollen showing the largest group-level increase. Warmer springs cause birch trees to begin catkin development earlier and sustain pollen production longer. This means sensitized patients in northern climates are experiencing higher cumulative pollen doses each year, which may drive higher new-sensitization rates and increased OAS burden in previously mild patients. Monitoring local NAB station data during your region's historical season dates is the most reliable tracking tool.

They are often the same allergy expressed in two tissues. Birch Bet v 1 and hazelnut Cor a 1 belong to the same PR-10 allergen family and share approximately 67 percent sequence identity. Patients sensitized to Bet v 1 via spring birch pollen exposure commonly develop cross-reactive IgE to Cor a 1, causing OAS when eating raw hazelnuts. This is different from primary hazelnut sensitization, where Cor a 9 (legumin) or Cor a 14 (2S albumin) are the relevant proteins — those drive systemic reactions independent of birch exposure. A component IgE test distinguishing Cor a 1 from Cor a 9/14 tells your allergist whether your hazelnut reaction is mild PR-10 OAS (birch-driven) or systemic-risk primary nut allergy.

Most patients notice some improvement in their first or second birch pollen season after starting subcutaneous immunotherapy, typically around 6 to 12 months into the buildup phase. Maximum benefit usually develops by year 2 to 3 of the maintenance phase. The treatment course continues for 3 to 5 years to achieve sustained disease modification — meaning the benefit persists for at least 3 years after stopping shots, rather than returning immediately as it would if you simply took antihistamines. Clinical trials by Bodtger (2002) and Arvidsson (2002) both demonstrated significant symptom-score reductions versus placebo groups receiving mock injections.

Yes. Subcutaneous immunotherapy (allergy shots) for birch pollen is offered to children typically from age 5 years onward, depending on the allergist's clinical judgment and the child's ability to communicate symptoms. Sublingual drops have been studied in children as young as 3 to 4 years in European trials. Immunotherapy in children carries a theoretical added benefit of potentially reducing the risk of developing new sensitizations (a phenomenon called 'allergen expansion prevention'), though this is not universally confirmed. A board-certified pediatric allergist should guide the decision based on the child's symptom severity, medication burden, and quality-of-life impairment.

Bet v 1 is the name of the major allergen protein in birch pollen — a 17.5 kDa PR-10 family protein produced by the birch tree. On a component-resolved allergy test (ImmunoCAP or similar), a high Bet v 1 IgE result means your immune system has produced antibodies specifically against this protein. Bet v 1 elevation is the most clinically informative birch result: it confirms primary birch sensitization and explains cross-reactive OAS to raw apple, cherry, peach, hazelnut, carrot, and soy. If your Bet v 1 is positive, cooked versions of those foods are generally safe. If your Bet v 2 (profilin) is also elevated, a broader range of foods and pollens may trigger symptoms.

No. Birch and oak are different tree species with overlapping but distinct spring seasons, and NAB stations count them separately. Birch season typically peaks in April and early May, while oak can extend from April through June depending on region. Both are Fagales-order trees with PR-10 cross-reactivity, meaning a patient sensitized to birch Bet v 1 may also test positive to oak Que a 1 by cross-reactivity. However, some patients are sensitized to oak but not birch, or vice versa — component testing can distinguish primary from cross-reactive sensitization. Most allergy panels test both birch and oak separately, and NAB station daily reports publish separate counts for the major tree pollen species.