Allergy and Pollen

What is hayfever?

Hay fever (seasonal allergic rhinitis) is an allergic reaction to pollen and spores. The symptoms include sneezing, runny eyes and nose, itching nose and sometimes headache and tiredness.

Which pollen types cause hay fever?

Grass pollen is the most frequent cause of hay fever but other types are also important including pollen from trees such as alder, hazel, birch and horse chestnut, and from weeds including plantains, mugwort and docks. A person suffering from hay fever may be allergic to one, several or many types of pollen. The relative importance of the kinds of pollen that can cause hay fever varies between different climatic and vegetation zones. For example in Scandinavia , Birch pollen is very prolific and is the most important type whereas in parts of southern Spain Olive pollen ranks as the main cause of hay fever. In Britain about 90 % of hay fever sufferers are allergic to grass pollen and about 25 % are allergic to birch pollen.

How important are fungal spores as a cause of hay fever?

Spores from fungi or moulds may produce hay fever in susceptible people but they are a relatively minor cause of seasonal symptoms. Most types of fungal spore that are likely to be culprits, such as Alternaria, Aspergillus and Cladosporium, are abundant in the atmosphere during the late summer and autumn.. In Britain over twenty different moulds are known to cause allergic reactions. An allergic person could be sensitive to just one or several of these. Many of the fungi involved can live indoors as well as outside and may be responsible for symptoms of rhinitis over many months resulting in perennial rhinitis rather than hay fever.

Is hay fever hereditary ?

All sorts of allergies tend to run in families. Children of parents with allergies are very likely to develop allergies themselves .If one parent has an allergy there is a one in three chance that any child will inherit it. However the allergy may not be in the same form. A parent with eczema or asthma may have a child who suffers from hay fever and vice versa. Modern research has been able to show that some members of a family may have an underlying tendency to allergy but are symptom free whereas other members have hay fever, asthma or eczema. The reasons for this are not entirely understood but it seems that exposure to any allergy producing substances , such as pollen , in infancy may increase the risk of developing an allergy in later life.

Is the incidence of hay fever increasing?

Hay fever is a modern disease. It was virtually unknown before 1800 and has become common only during the last hundred years. The first case to be described medically was in 1819 but the causes of the disease were not identified until 1873. Medical statistics show that the incidence of hay fever rose steadily during the nineteenth century in many countries including France, Germany and the United States. The numbers of people affected by hay fever have continued to increase since 1900 and it has become prevalent in countries, such as Japan ,where it was unknown 40 years ago. It has been suggested that the statistics do not show a real increase but just record the fact that nowadays people recognise hay fever and to do something about it . Although this may be true to some extent it cannot account for the vast increases reported from numerous countries.

Is hay fever worse in areas with high concentrations of air pollution ?

Some research suggests that certain types of air pollution make hay fever worse but the evidence is not clear-cut. Studies in many countries including Sweden, Italy and Spain have shown that hay fever rates are greater in cities than in the surrounding rural areas where pollen counts are higher. In Japan the highest incidence of hay fever was found in populations living along busy roads indicating that vehicle exhaust was involved. This is likely since diesel particles have been shown to make people more susceptible to allergens . Also high concentrations of nitrogen dioxide and sulphur dioxide can irritate the nose and airways. Some types of photochemical pollutants are more abundant in the countryside. For example, high concentrations of ozone occur in rural areas and can effect breathing even in healthy people .Research suggests that it makes the symptoms of hay fever worse but many other aspects are involved such as lifestyle and diet. More work is needed to sort out the relationships between air pollution and allergies.

What can I do to avoid getting hay fever ?

Although inheritance is important environmental factors also influence the development of hay fever. The best advice is to avoid exposures to high concentrations of pollen or spores. These may sensitise a person predisposed to allergy. They will not react to it on this first encounter but will have hay fever on subsequent exposures. For example people from northern Europe can develop allergy to Olive pollen if they are exposed to high concentrations during visits to the Mediterranean. At home exposure can be reduced by avoiding areas of pollinating plants and by keeping doors and windows shut on high pollen count days. It also helps to avoid air pollution and tobacco smoke that may irritate the nose and airways making them more susceptible to allergens. Several precautions can be taken in pregnancy and the early months of life to help prevent allergies. Smoking during pregnancy seems to increase the risk of allergies developing in the baby . Similarly exposure to high pollen counts and viral infections in the early months of life seems to increase the risk of developing hay fever. Low risk months for birth are those just after the pollen season whereas the high risk time is in the pollen season itself and two to three months before. Breast feeding is thought to help prevent allergies.

The effects of early exposure are strongest for birch pollen but it is also evident for grass and weeds.

What can I do to control the symptoms ?

The symptoms of hay fever can be controlled in two main ways. One is to avoid the allergens and the other is take medication. Pollen and spores spread over wide distances on the wind and penetrate into houses and vehicles. It is extremely difficult to avoid contact with them completely. Sensible precautions can be taken such as wearing dark glasses to keep pollen out of the eyes, keeping doors and windows shut and avoiding places with where the pollen count is likely to be high. The worst times for grass pollen are early morning to about 10 am and then in the late afternoon and evening (unless it's raining). In most cases the symptoms of hay fever can be controlled by medication. A wide range of treatments is now available including antihistamines, decongestants and corticosteroids. Some products, such as nasal sprays and eye drops are useful if a person has localised symptoms but antihistamines are the most common form of treatment for multiple symptoms. Certain treatments need to be started before the pollen season begins in order to prevent the onset of symptoms. Some remedies are available only by prescription but many can be bought over the counter at pharmacies. In all cases it is best to discuss appropriate treatments with a pharmacist or doctor.

What use is the pollen count and forecast ?

The pollen count is a measure of the number of pollen grains of a certain type per cubic metre of air sampled , averaged over 24 hours. The reported counts are usually for grass, birch and nettles and refer to the previous 24 hour period up to 9am that day. The pollen counts show when the various seasons start and end as well as the day to day variation in the amount of pollen in the air. This information can be used as a guide both to diagnosis and to the timing of treatments. For example the start of the grass pollen season in Britain can differ by about 32 days according to the weather in the spring and early summer. The pollen count indicates when prophylactic treatment should be started and when medication can be stopped at the end of the season. The daily pollen forecasts can be used to warn sufferers of adverse conditions so that they can modify their activities and take medication as required.

Are people with hay fever more likely to suffer from other allergic conditions such as eczema and asthma ?

If some-one has hay fever then the allergy to pollen may also be present in different forms. Only a minority of people with hay fever develop pollen asthma as well. Those who do have hay fever and pollen asthma find that the asthma attacks occur later in the pollen season than the hay fever symptoms and continue for longer after the peak pollen counts. This suggests that a longer exposure time is necessary. Hay fever sufferers may also have urticaria ,or nettle rash, through direct contact with grasses on the skin. The allergens that cause the hay fever are present in the grass sap and may produce large itchy bumps on the skin in an allergic reaction .The same effect can happen if pollen antigens enter the blood stream, such as through the tiny blood vessels in the nose, and reach the skin by this indirect route. A minority of people with hay fever have an allergic form of eczema that is aggravated by contact with pollen and other plant material bearing allergens. Research suggests that people who are allergic to several substances tend to have stronger allergic reactions. For example work in Japan found that people who are already allergic to house dust mites tend to have stronger reactions if they then develop hay fever than people who do not have other allergies.

Last update February 2008