Itchy eyes and sneezing are the common symptoms of an allergy, but some people react in a much more severe way, sometimes suffering acute asthma attacks and even anaphylactic shock.

According to John Collard, clinical director of charity Allergy UK, allergies have never been so prevalent, with one in three people in the country having some form of allergy – 20 million people including 40 per cent of children of school age.

"There are many theories as to why children and adults are suffering more allergies than 20 years ago," he says.

"There is growing weight behind the hygiene hypothesis. The theory is that the immune system likes to develop tolerance to things it is exposed to in very low levels. If you aren't exposed to these things as a child, it is more likely that you will develop an allergy to it."

Mr Collard said children who grew up on farms and were exposed to high levels of bacteria have fewer allergies than those children brought up in homes, cleaned with anti-bacterial sprays.

Second and third children are also less likely to have as many allergies as first-borns as they are exposed to bacteria brought home by their elder sibling.

As a result, asthma and eczema have increased over the last couple of decades.

Mr Collard said commuters were also at higher risk of developing an allergy.

"There is evidence that increased exposure to chemicals, such as exhaust fumes, increases the likelihood of someone developing an allergy to grass pollen," he said.

"There is grass all along the road side and the pollen gets into the car and stays there. Its effect is then increased by the traffic fumes. Commuters have 10 times more pollen in their cars than on a high pollen count day outside."

On the face of it, having a runny nose and itchy eyes may not sound like the end of the world. But John Collard says even these milder symptoms can have major implications on people's lives.

One man contacted Allergy UK as he had been threatened with the sack as his red eyes and sneezing was putting off customers.

"People do not take their anti-histamines until it is too late. The longer you leave an allergy the more severe the symptoms will become," says Mr Collard. "That is why it is very important to treat the symptoms straight away. With hay fever, it is important to start taking the medication a few weeks before your symptoms normally start."

Mr Collard said it is often quite difficult for people to get adequate treatment for moderate allergies and that is why Allergy UK has teamed up with Nuffield Health.

They have opened allergy clinics at Nuffield Health's hospitals, including Leeds.

People can refer themselves for a consultation and a test conducted by an allergy nurse from £140.

A spokesman for Nuffield Health says: "Apart from the test, each patient will receive advice and information, plus one year's free membership to Allergy UK who will provide information and support in the coming year".

Before any test is carried out, an allergy nurse takes a detailed medical and home history, which can often identify what people are likely to be allergic to.

I have always suffered from hay fever and also I sometimes get sore eyes when I go near our cat.

Nuffield Health allergy nurse Linda Guillardine was able to select a number of allergens which she could introduce me to using a skin prick test. She also added a negative and positive control containing histamine.

Almost immediately I felt a reaction to one of the allergens as a small raised area, like a nettle sting, appeared on my forearm which itched madly.

After 15 minutes, Linda measured the raised area. Surprisingly, I had no reaction to the grass and tree pollen, meaning that I am probably sensitive to the sap rather than allergic to the pollen.

The allergen I responded to most was actually cat – which can help people when deciding whether to introduce that type of animal into their home.

You can make an appointment for an allergy test by calling 0845 6026442.