What causes allergies
Season
Hay fever is the most obvious example, but further analysis of the exact timing of symptoms may identify what type of pollen is responsible.
Grass pollen is usually at its height of production, depending on the weather, during June, whereas tree pollen occurs earlier. Occasionally we have seen symptoms for a very brief period in the summer, possibly as short as one week, and in this situation a single plant pollen, produced at this time, is responsible.
Moulds are also seasonal, but different species produce spores at different times all year round. Spores are released in response to wet weather, especially after a dry period, so autumn and spring are the worst seasons.
Frost kills fungi, so a cold winter spell reduces the spores released, and people allergic to spores will notice their symptoms lessen when there are overnight frosts.
Another allergy showing seasonal variation is that to house dust and house dust mite. During the winter ventilation is reduced, central heating is switched on and we go out less. The warm, damp atmosphere in our houses produces ideal conditions for the house dust mite to thrive, and there is more human contact.
Location
Where symptoms are worse can give clues which are as important as when. A condition which appears worse inside rather than outside is probably due to house dust or chemicals – if worse outside moulds or pollen are the likely cause. If symptoms seem worse at work, the possibility of chemicals or animal exposure must be considered. Clearly if there are pets in the house, and symptoms occur only at home, animal dander sensitivity is likely.
The location of the home may be important, particularly if the illness has worsened since a recent move, as shown by the following example.
Occupation
Any occupation which exposes one to high levels of a possible allergen may lead to sensitization to that substance, with subsequent reaction even when exposed at low levels. Vets, for example, may become allergic to animals, and hairdressers to the chemicals they use. Even if they leave their job, contact through everyday items may perpetuate the problem. Clearly for clues from a person’s occupation to be useful, a knowledge of what substances are encountered is essential.
Hobbies
Some people have unusual hobbies which put them in contact with possible sensitizing items. Amateur artists may develop a sensitivity to paint fumes, and evening electronic technicians may react to fumes from solder. In this area much the same information can be gained as from investigation of occupation.
Diet
People can develop symptoms due to recent dietary change, when there may have been an increase in some foods, due, for example, to changing to vegetarian habits. In addition food ‘fads’ may develop, causing a high intake of a particular food.
Frequently the food which is the underlying cause of a problem is a food to which the individual is almost addicted. Indeed, if there are no means available for testing, the most effective way of identifying an allergenic food is to ask ‘what food would be most missed’ – as there is often a craving for the food which is, in fact, harmful
