Trees provide us with many miracle cures, most famously aspirin from the willow and the cancer-busting drug taxol from the yew. However, they can also affect human health negatively. Pollen from the silver birch, Betula pendula, is the second most severe allergen for people in the UK. Late March is the usual peak in birch pollen levels so many people with ‘hay fever’ are likely to be suffering at the moment.
Birch pollen grains are tiny, typically 20 microns (0.02mm) across, and can travel hundreds, if not thousands, of miles in the atmosphere. A recent study that assessed birch pollen levels for Londoners concluded that their concentrations were likely to be heavily influenced by birch forests in southern England and continental Europe, not only local street trees.
Birch pollen is also strongly associated with allergic reactions in the mouth to certain foods. This is termed pollen-related oral allergy syndrome (OAS). Sensitivity to birch pollen is related to OAS when eating almonds, apples, apricots, avocados, bananas, carrots, celery, cherries, chicory coriander, fennel, fig, hazelnuts, kiwi fruit, nectarines, parsley, parsnips, peaches, pears, peppers, plums, potatoes, prunes, soy, strawberries, wheat, and potentially walnuts. As many as 75% of birch pollen-allergic people may be affected by the mildest form of OAS, a sensation in the lips or tongue after eating raw apples. However, many sufferers do not realise that they have an allergic problem.
I came across an interesting account by a Swede who reports his own solution to battling a birch pollen allergy by drinking birch tree sap, including instructions on how to tap a tree for its sap: read more. I’m not a medical man so I can’t comment on this except to say that this definitely intrigued me.