The UK Pollen Calendar
Tree, grass, weed and fungal spores arrive at different times of year. Which months are bad for you is what identifies which one is yours.
Part of the Complete Hay Fever Guide.
Key fact: “Hay fever season” is really three overlapping seasons caused by three different pollens, plus fungal spores in autumn. Which months are bad for you identifies which one is yours — and that is something you can work out without a test.
Three seasons, not one
People describe hay fever as though it were a single block of the year, and it is not. Three distinct pollens are released at different times by different plants, and a fourth trigger — fungal spores — arrives after all of them. Someone who is miserable in April and fine in June has a completely different allergy from someone whose worst fortnight is the middle of June, even though both will call it hay fever.
Knowing which is yours is useful for ordinary reasons: knowing when to expect it, knowing whether a bad August means your grass allergy is getting worse or that something else is going on, and knowing whether a holiday in a particular month is likely to be affected.
The calendar, month by month
| Pollen | In the air | Peaks | Share of UK hay fever |
|---|---|---|---|
| Tree | Late March to mid May | Birch, through April | A minority — but birch in particular affects people severely |
| Grass | Mid May to July | Two peaks: early June and early July | Around 95% — by far the largest group |
| Weed | Late June to September | Variable through late summer | Nettle, dock and mugwort. Often assumed to be a long grass season |
| Fungal spores | July into autumn | Warm, damp spells | Commonly missed altogether, and the usual explanation for autumn symptoms |
The seasons overlap at their edges, which is why a bad spell in late May can be the tail of the tree season, the start of the grass season, or both at once.
Working out which pollen is yours
Two or three seasons of paying attention to the timing will tell you, and the patterns are distinctive enough to be useful.
- Bad in April, better by the end of May — tree pollen, most likely birch.
- Bad from late May through July, worst on warm dry days in June — grass. This is the common one by a wide margin.
- Bad in August and September — weed pollen or fungal spores rather than grass, which has finished by then.
- Bad in autumn, particularly in damp weather or around fallen leaves and compost — fungal spores.
- Bad all year, with a seasonal worsening on top — something perennial underneath. Our guide to year-round allergies covers what that usually turns out to be.
The birch and raw fruit connection
There is one cross-check that points quite firmly at tree pollen, and most people who have it do not know it is connected.
Many people allergic to birch pollen get itching or tingling of the lips, mouth or throat when eating raw apple, cherry, peach, plum, carrot, celery or hazelnut — which settles within minutes and does not happen when the same food is cooked. This is oral allergy syndrome. The proteins in those foods are shaped closely enough like birch pollen protein for the immune system to confuse them, and cooking changes the shape enough to stop the reaction.
It is usually mild and confined to the mouth. It is worth mentioning to a clinician, both because it identifies your pollen and because a small number of people react more significantly.
Anything beyond mouth itching is different. Swelling of the lips, tongue or throat, difficulty swallowing or breathing, or a widespread rash after eating is not oral allergy syndrome and needs urgent medical assessment.
Why the same count feels worse later in a season
A pollen count that was tolerable in May can be miserable in July, and the reason is biological rather than meteorological. Repeated exposure to an allergen makes the lining of the nose progressively more reactive — a process called priming — so that as a season goes on, less pollen is needed to produce the same symptoms.
It explains a pattern people often misread as the allergy worsening year on year, or as a medicine losing its effect. Neither is usually the case. The nose is simply further into a season than it was the last time you compared.
Weather, time of day and pollen counts
| Conditions | What happens to pollen |
|---|---|
| Warm, dry and breezy | Highest counts. Pollen is released and carried furthest |
| Morning, rising through the day | Pollen is released early and rises as the air warms, settling again as it cools in the evening |
| Heavy, sustained rain | Washes pollen out of the air — the genuine relief people notice |
| Short summer thunderstorm | The opposite. Humid downdraughts pull pollen down and burst the grains into far smaller fragments. This matters a great deal if you also have asthma — see hay fever and asthma |
| Coastal, with an onshore breeze | Lower counts, which is why the seaside genuinely helps some people |
| Cities | Counts are often lower than in the countryside, but air pollutants can worsen the response to what is there |
The Met Office publishes a daily pollen forecast for the UK through the season, broken down by region, which is more useful than a general count once you know which pollen you are watching for.
Reducing what reaches you
None of this is a substitute for treatment, but on a high-count day it lowers the dose your nose has to deal with.
- Shower and change clothes when you come in. Pollen travels home in hair and on fabric and then spends the evening with you.
- Dry washing indoors through your season. A line of bedding outdoors in June is a pollen trap you then sleep in.
- Keep bedroom windows shut in the early morning and the evening, when counts are rising and falling.
- Wraparound sunglasses measurably reduce how much pollen reaches the surface of the eye.
- A smear of petroleum jelly around the nostrils traps some pollen before it is breathed in.
- Keep car windows closed and use recirculation; a cabin pollen filter helps if the car has one.
- Get someone else to mow the lawn. Mowing releases a large amount of grass pollen at face height.
Frequently Asked Questions
When is hay fever season in the UK?
There are three, overlapping. Tree pollen runs from late March to mid May, peaking with birch in April. Grass pollen runs from mid May to July with peaks in early June and early July. Weed pollen runs from late June to September. Fungal spores follow from July into autumn. Grass is responsible for roughly 95% of UK hay fever, so for most people the season is mid May to July.
When is grass pollen season in the UK?
Mid May to July, with two peaks that typically fall in early June and early July. Counts are highest on warm, dry, breezy days. Pollen is released in the morning and rises through the day as the air warms, settling again in the evening as it cools.
Why do I only get hay fever in April?
Almost certainly tree pollen, and most likely birch, which is the dominant tree allergen in the UK and peaks through April. Tree pollen is in the air from late March to mid May, so symptoms that start in spring and have gone by the end of May point firmly at trees rather than grass.
Does rain help hay fever?
Heavy, sustained rain does, because it washes pollen out of the air and counts fall for as long as it lasts. A short summer thunderstorm can do the opposite: humid downdraughts pull pollen down to ground level and rupture the grains into much smaller fragments that reach deeper into the airway. That is a particular concern for anyone who has asthma as well as hay fever.
Why does raw apple make my mouth itch?
This is oral allergy syndrome, and it points towards birch pollen allergy. The proteins in raw apple, cherry, peach, carrot, celery and hazelnut are shaped closely enough like birch pollen protein for the immune system to confuse them. Cooking changes the shape, which is why cooked apple is usually fine. It is normally mild and confined to the mouth, but swelling of the lips, tongue or throat, or difficulty breathing, is something different and needs urgent assessment.
References
- NHS. Hay fever. nhs.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Allergic rhinitis. cks.nice.org.uk
- British Society for Allergy & Clinical Immunology. BSACI guideline for the diagnosis and management of allergic and non-allergic rhinitis. bsaci.org
- Joint Formulary Committee. British National Formulary: antihistamines, allergen immunotherapy and allergic emergencies. bnf.nice.org.uk
- electronic Medicines Compendium. Summaries of Product Characteristics. medicines.org.uk
- Met Office. Pollen forecast and the UK pollen calendar. metoffice.gov.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Allergy medicines differ in how much drowsiness they cause and in who can take them, and decongestant nasal sprays are not for long-term use. If you have asthma, breathing symptoms that worsen alongside hay fever need review rather than more antihistamine. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.