It’s that time of year. The time when we don sunglasses to hide our streaming eyes, and are perpetually drugged up to or eyeballs with anti-histamines- but what is hayfever exactly and what causes it?

Hay fever is a inflammation that happens- mostly in our eyes and nose, when our immune systems over reacts to pollen in the air. It affects more than 400 million individuals world wide!

The culprit: Pollen

Pollen is a powdery substance used to transfer male genetic material from the anther of a flower to the stigma of another flower (cross-pollination), or to the stigma of the same flower (self-pollination).

Pollen comes in many different shapes and sizes, but you wouldn’t be able to see these differences until you look at the pollen grain under a microscopic. Because pollen grains are so tiny they can  be blown around in the wind super easily, and can easily get up our noses, and in our eyes and mouth causing inflammation.

Hay fever is an allergic reaction.

A mostly forgotten fact about allergies is that you can develop them at any point.  This means that if you are in your 50s and never had hayfever in your life, you could wake up one spring with awful hayfever! The human body is great right?!

Important side note- this is why it is so important for people who colour their hair to do a allergy patch test every single time. A lot of allergies develop over time with repeat exposure.Just because you didn’t have an allergy last time you had your hair coloured does not mean you are safe the next time.

What happens when you have an allergic reaction?

Allergies are caused by the immune system misidentifying otherwise harmless substances as harmful. This causes the immune system to launch a full scale attack against the allergen, normally at a level far greater than required.

White blood cells, called Lymphocytes, are a major component of the immune system, and are the chief culprits in starting the allergic response.

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The 5 major groups of white blood cells. Lymphocytes and Basophils are major players in the Immune response (Image source: DOI:10.15347/wjm/2014.010.)

There are two types of lympocyte: B-Cells and T-Cells. Normally these lymphocytes guard your body against bacteria, viruses and toxins. They work by checking everything they encounter in your body- from cells to particles, to make sure it is ok to be in your body. If they come into contact with anything threatening they flag it identifying it as a foreign invader. After a B-Cell identifies a foreign invader it heads back to a lymph node where it changes into a plasma cell to start producing antibodies to fight the threat.

There are 5 types of antibodies, called immunoglobulins: IgA, IgD, IgE, IgG and IgM.  IgE is the antibody responsible for the allergic response.

The problem with allergies is that the B-Cells identify invaders incorrectly- identifying for example, inhaled pollen particles as an invader- even when it isn’t! This in turn means that lots of the IgE antibody is produced for that allergen particle. This is known as the ‘sensitising period’.

The IgE antibody attaches to mast cells and basophils- two other types of white blood cell, throughout the body. Crucially, it takes between a week and 10 days of sensitising exposure to the allergen before the mast cells and basophils to be ‘primed’ for attack by IgE antibodies.

If the allergen then comes along again- the mast cells and basophils launch a full assault, triggering the allergic response.

320px-Mast_cells

Diagram of the allergic response against Ragweed, which is one of the biggest causes of hayfever in North America (image source: Wikimedia)

Mast cells and Basophils contain histamine a allergy mediator. When mast cells and basophils attache to identifying markers on the ‘invader’ allergen particle, this causes the  cells to be destroyed relasing all the histamine and other allergy mediators contained within into the blood stream.  And this causes havoc!!

Histamine causes lots of different things to happen- in particular a dilation of blood vessels and a drop in blood pressure. This dilation causes spaces, which fill with fluids- leading to the swelling often seen in allergic responses. This also leads to the allergic responses of itching, hives, sneezing- and in extreme cases nausea, diarrhea and extreme inflammation leading to anaphylatic shock.

The best way to avoid getting a allergic reaction (once identified as such) is to avoid whatever it is you are allergic to. The problem is you can’t really avoid pollen… Fortunately, there are a lot of medications which can be used to help reduce hay fever symptoms including anti-histamines and decongestants.  And, more often than not, you will only suffer with your hay fever for short periods of time through the year- depending on when the plant you are allergic to is pollinating.

The big hay fever inducing culprits are:

The Alder tree- Pollen is released from the end of January, peaking in March. If you are sensitive to alder pollen you may also suffer with hazel and birch pollen is in the air…

Ash trees- Release pollen for about two weeks, between March and April.

Birch trees– Produce one of the most allergenic pollens! Pollen begins being produced around the middle of March.

Oak trees (My personal nemesis)-  release pollen in April and May.

Interestingly, two poor plants are nearly always blamed for hayfever- but may not actually be the cause!

Oil seed rape– maybe its because of its bright yellow flowers, but oil seed rape is often blamed as the cause of hayfever. In fact, the pollen produced from this plant has a low allerginicity- meaning its probably not the cause of your hayfever.

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Oil Seed Rape: source pixabay

Grass– It just so happens that the grass starts to get cut at the same time that hayfever begins to affect people- but grass doesn’t actually start producing pollen in high amounts until late may-june. So, if your hayfever gets really bad in April its most likely not the fault of grass, but rather one of the pesky trees listed above!

References:

https://www.benadryl.co.uk/understanding-allergies/uk-allergy-calendar

https://www.zyrtec.com/allergy-guide/outdoor-allergies/pollen-allergy-type-by-season

https://health.howstuffworks.com/diseases-conditions/allergies/allergy-basics/allergy4.htm 

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