Hay fever: Do allergies change over time?

Many people find their hay fever symptoms dwindle as they age, although no one knows why. But allergies can and do get worse over a lifetime, and there are reports of people who are middle aged and older suddenly developing hay fever having never been sensitive to pollen before. It’s also true that if you’re unfortunate enough to have one allergy, you are more likely to develop others. This is in part down to basic biology: some people simply have an immune system that is more allergy-prone. “If you’ve got an allergy, you’ve got that combination of genetic susceptibility plus environmental exposure, and it’s that combination that produces an allergy,” says El-Shanawany. Not only that, immune cells sensitised to one allergen can cross-react with other related proteins, meaning allergies can “spread”. For instance, some of the proteins in birch pollen are closely related to those in alder and hazel, which peak around a month earlier, potentially prolonging the agony for someone sensitised to birch. Foreign travel is another thing that can foster the development of new allergies. “If you travel to southern Spain in spring and there is a lot of olive pollen then you could become sensitised to it within days,” says Emberlin. “Olive pollen cross-reacts with ash, so you might come home and find that you start getting a reaction to ash trees.” It’s not just other pollens you can find yourself sensitised to if you have hay fever – the condition can trigger cross-reactions to foods. For example, a birch pollen allergen called Bet v 1 shares similarities with proteins in some fruits and nuts, and so people with hay fever may occasionally notice swelling and itching in their mouth when they eat uncooked fruits like as apples, peaches and kiwi. Hazelnuts, almonds or even soya milk can trigger it too. Similarly, people with an allergy to house dust mites may find they develop reactions to crustaceans. This is called oral allergy syndrome, and is usually harmless – but not always. One study found that oral allergy symptoms spread to other areas of the body in nearly 9 per cent of people with the condition, and progressed to anaphylactic shock in 1.7 per cent of them. Then there’s asthma. Hay fever is a disease of the upper airways whereas asthma is one of the lower, characterised by inflammation, muscular contraction and the production of mucus. However, having hay fever roughly triples the risk of developing asthma and there’s a growing sense that the two conditions are different manifestations of the same disease. “If you have uncontrolled hay fever and you are reacting to pollen, a chemical cascade is developing in your nose and to some extent in the rest of your body that can ultimately recruit reactions in the lungs,” says Emberlin. “You will get a tendency towards having asthma.”

New Scientist, 13 April 2015 ;http://www.newscientist.com/ ;