A number of different allergens trigger allergies in people, with some of the most common including pollen, dust, mould and pets.
The Weatherzone Pollen Index measures the potential for pollen to trigger allergic reactions in susceptible people. Pollen levels in the atmosphere will be highest on hot days and on days where a dry wind is blowing. Additionally, light rain overnight or during the early morning will also cause high pollen levels. These are the days when you will experience the telltale symptoms of a runny nose, watery eyes, itchy skin and nasal congestion.
EXTREME: Most sufferers of pollen allergies will experience symptoms on extreme pollen level days. Symptoms may be severe in some sufferers. These days typically occur as a result of high temperatures and/or dry, hot winds, so the best precaution is to stay indoors.
VERY HIGH: Most sufferers of pollen allergies will experience symptoms on very high pollen level days. These days are typically warm and dry so the best precaution is to stay indoors away from sources of pollen.
HIGH: Some sufferers of pollen allergies will experience symptoms on high pollen level days, but these are unlikely to be severe. Temperatures are likely to be warm on these days, but there may be a limiting factor such as rain or sea breezes.
MODERATE: A few sufferers of pollen allergies may experience symptoms on moderate pollen level days. These are typically cooler days or days on which rain is expected to "flush" the pollen out of the air.
LOW: Very few sufferers of pollen allergies would be expected to experience symptoms on low pollen level days. These are typically either cold or wet days when there is likely to be little pollen released into the atmosphere.
04:14 EDT It's not easy to get a sense of just how powerful a typhoon, cyclone or tornado will be.