POTENTIAL ALLERGENS: POLLEN AND HOUSE DUST
Pollen
Mostly causes seasonal rhinitis (hay-fever). The timing of the symptoms will depend on the type of pollen at fault: February-May, with the peak in April, for tree pollen, June-July for grass pollen and July-August for weeds such as nettles, golden rod and mugwort. Pollen can also cause asthma. Where there is sensitivity to perennial allergens as well, the rhinitis may persist all year but get worse in spring or summer. ‘Hay-fever’ that begins in late July or August and continues into the autumn is more likely to be mould allergy.
In some people, certain foods can heighten sensitivity to pollen. Foods eaten only in summer (or in greater quantities then) can produce symptoms that may resemble hay-fever – suspect summer fruits, orange squash and ice-cream.
Human skin scales or other components of dust may be the problem, but more often it is the house-dust mite, Dermatophagoides (‘the skin-eater’). This minute animal lives on flakes of human skin shed by all of us in great quantities. It is not an insect, as is often stated, but a mite – a
distant relative of the spiders. Because it is not an insect, it is not killed by most insecticides. Some people react to the mites themselves but most are allergic to the faecal pellets (droppings). These are covered with a thin layer of protein produced by the mite, and it is the protein that acts as an allergen. House-dust mites thrive in dusty houses, old sofas and interior-sprung mattresses – foam mattresses are less of a problem. Sunshine and dry air are the mite’s greatest enemies, so it prefers fitted carpets cleaned with a vacuum cleaner, to loose rugs or carpets that are taken outside, beaten and left to hang in the sun for a while. Damp weather favours the mite so there may be a seasonal variation in the severity of attacks (note that damp also favours moulds). Shampooing a carpet can stir mites up and provoke an attack – especially in children playing on a carpet. Sensitivity varies: some people can obtain relief simply by discarding an old mattress or sofa, others require the house to be scrupulously clean, and free of all fitted carpets and upholstery.
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