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If you have hay fever, you're probably allergic to pollen. That's why you get symptoms in the spring, summer or fall, when there's lots of pollen around.

Hay fever can make you feel miserable. You sneeze a lot and your nose runs or feels stuffed up. Your eyes may be red, itchy or watery. And you may have a cough or a wheeze.

You may get hay fever so badly that you can't sleep, can't concentrate and find it hard to work. And at certain times of the year, pollen is hard to avoid. But there are good treatments that can help you feel better. You may need to start treatment before the pollen season begins and before you get symptoms.

Hay fever is also called seasonal allergic rhinitis or intermittent allergic rhinitis.

• If you have hay fever, you're probably allergic to pollen.
• Some people with hay fever are allergic to mold.
• You get hay fever at times of the year when there's lots of pollen or mold around.
• If you have hay fever, it's a good idea to avoid pollen or mold as much as you can. (To find out more, see Avoiding pollen and mold.)
• Treatments can help get your hay fever under control.
• The good news is that hay fever may go away as you get older.^{1 2}

To understand why you get an allergy like hay fever, it helps to know a little about your immune system.^{3 4}

• Your immune system helps protect you from things that can make you ill, such as bacteria and viruses.
• Your immune system is made up of lots of special cells.
• These cells are found all over your body, including inside your nose, at the back of your throat and in your lungs.
• The ones in your nose, throat and lungs are there to protect you against the kinds of infections you can get in your airways, such as colds or pneumonia.

Hay fever is an allergy. You have an allergy when your immune system has an abnormal reaction to something that's normally harmless.

It mistakes something harmless for something that is harmful and tries to attack it or get rid of it. And this gives you symptoms such as sneezing, a stuffed-up nose, and itchy or watery eyes.

Most people with hay fever are allergic to pollen.⁴ Plants release pollen in the spring, summer or fall. Pollen is like a very fine dust, and you can't always see it.

But some people with hay fever are allergic to mold. Mold is a type of fungus that grows in damp, shady places. Its seeds are called spores. Like pollen, these spores are carried through the air.

To learn more, see More about what happens in hay fever.

When you have hay fever, breathing in exhaust fumes, cigarette smoke or perfume may make your symptoms worse.⁵

There are many different types of pollen. Pollen is released by different plants at different times of the year. Most people with hay fever are allergic to the pollen made by trees, grasses or weeds. You may be allergic to only one type of pollen or to more than one.

• Pollen from ragweed is the most common trigger for hay fever. Ragweed grows by the side of the road, in empty lots and in fields.⁶
• In most parts of the United States, ragweed releases pollen in the fall. So if you're allergic to ragweed, this is when you'll get symptoms of hay fever.

Plants like ragweed release huge amounts of pollen into the air. That makes pollen very hard to avoid. And in the United States, there are lots of plants that cause allergies.⁷

To find out more, see Plants that give you hay fever.

Outside, you can find mold on rotting logs and fallen leaves, in compost piles and on certain grasses and weeds. Mold can also grow on damp spots inside your house, such as in your basement.⁴ There are thousands of different types of mold, but fortunately, only a few cause allergies.^{2 4}

You may be able to help yourself by figuring out when you're most likely to get symptoms of hay fever. This can help you be ready. For example, you need to start using some treatments before there's pollen or mold spores in the air. (To find out more, see Steroid nasal sprays.)

You can get symptoms of hay fever at any time of the year when pollen or mold spores are around, which could be in the spring, summer or fall. Exactly what time of year you get them depends on what you're allergic to and where you live.

• Pollen: Generally, the farther north you live, the later pollen is released. So if you live in New York, for example, you'll probably get hay fever symptoms later in the year than someone who lives in Florida.⁴ To find out more about the pollen season where you live, see our Pollen maps.
• Mold: If you're allergic to mold, you may have symptoms from spring to late fall. And your symptoms may be at their worst from July to late summer.⁸

You've probably heard of pollen counts or pollen forecasts. They're often mentioned in weather reports. They tell you how much pollen is in the air.

The pollen count is usually measured in grains of pollen per square meter of air, based on an average collected over 24 hours. (A meter is a bit longer than a yard.) The count can be low, moderate or high. The higher it is, the more likely it is that people with hay fever will get symptoms.⁴ So you can use pollen forecasts to help you predict the days when you're likely to have symptoms.

Pollen counts tend to be higher on warm, dry, breezy days and lower on cold, wet days.⁸

The National Allergy Bureau monitors pollen counts in many areas of the United States.⁹ You can call their toll-free number to see what the count is in your area: (800) 9-POLLEN.

Pollen levels are usually highest early in the morning, between 5 a.m. and 10 a.m. So that's the worst time to be outside if your hay fever is triggered by pollen.

If you have hay fever, you may also be allergic to things besides pollen or mold. Two of the most common triggers for allergies are dust mites and furry pets such as cats and dogs.⁸ Allergies to these things can give you symptoms similar to hay fever.

If you have an allergy that gives you a runny nose or a stuffed-up nose, or an allergy that makes you sneeze, your doctor may call it allergic rhinitis.¹⁰ There are two main types. Many people get both types.

• Seasonal (or intermittent) allergic rhinitis: This is hay fever. You have this if you're allergic to pollen or mold and you only get your symptoms at certain times of the year.
• Perennial (or persistent) allergic rhinitis: You have this if you're allergic to something like dust mites or pets. Your symptoms last most of the year.

You can get other allergies along with hay fever. Two common ones are:

• Eczema, a condition that makes your skin dry, red and itchy
• Asthma, a condition that makes you cough and wheeze. Most people who have asthma also have allergic rhinitis.¹¹

To find out more, see Eczema, Asthma in adults and Asthma in children.

If you have an allergy like hay fever, you may think you have a cold. The symptoms can be similar. But it's important to know the difference between them. The treatments are different, and if you have hay fever and the symptoms are bothering you, treatment may help.

Here are some of the differences between having hay fever and having a cold.¹² But if you're not sure which you have, it's a good idea to check with your doctor.

Certain things make it more likely that you'll get hay fever. These are called risk factors.

Two of the main risk factors for hay fever are:¹³

• Having someone in your family who has allergies.
• Having other allergies, for example to dust mites.

Having risk factors doesn't mean you'll definitely get hay fever. It just means that you're more likely to get it.

To find out more, see Risk factors for hay fever.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.