In 1819, a London doctor called John Bostock published an account of "an unusual train of symptoms" from which he suffered periodically - itchy and watery eyes, a runny nose and persistent bouts of sneezing.
Once identified, the ailment was observed to be a prevalent one, and became known to the medical fraternity as "Bostock's catarrh".
Then it was discovered that the condition was an allergic reaction to pollen in the atmosphere, and that pollen from the various grasses was the worst offender - and so it came to be "hay fever".
Concentrations of pollen tend to be high outdoors from the middle of May to early August, reaching a maximum during June and early July.
The worst culprits for producing spores are the wind-pollinated plants, such as grass, ragweed and birch trees, which must release vast amounts of pollen to ensure that some will reach their targets; insect-pollinated plants, on the other hand - those with colourful flowers or strong scents - produce far less pollen.
The amount of pollen in the air at any given time depends on several meteorological factors.
First of all, the extrusion of pollen by plants - a process called anthesis - shows a variation throughout the day which is related to temperature and light intensity. Second, the extent to which the pollen particles, once expelled by the plant, are collected by the air, depends on the wind strength at the time. In relatively calm conditions, the pollen is shed slowly, and is less likely to become suspended in the air; it falls directly to the ground instead.
Another important factor is the degree of instability present in the atmosphere - the extent to which there is a tendency for vertical currents of air to develop.
If there is a great deal of vertical motion, it may be sufficient to disperse the pollen throughout a deep layer of the atmosphere, thus reducing dramatically the count near ground level.
But perhaps the greatest effect is caused by rain; a shower of rain "washes" the air and significantly reduces the pollen concentration. Heavy rain may even disrupt the process of anthesis altogether.
The pollen content of the air is measured by means of an instrument called a spore trap, which draws air through a narrow opening in such a way that the spores impact with a sticky microscopic slide.
Forecasts of likely pollen levels are carried out by feeding all the relevant parameters, including meteorological predictions, into a computer program which carries out computations based on known relationships between them all. The end result is a "pollen count" prediction for the following day.