Millions of hay fever sufferers across Britain are bracing for a difficult week ahead as the Met Office has declared a “red alert” warning for pollen levels.Elevated tree pollen concentrations struck England on Monday and are forecast to persist until next weekend, according to forecasters.The warning represents the highest severity level on the Met Office’s pollen scale, indicating that the vast majority of those with pollen allergies will experience symptoms.Approximately 10 million people in England are affected by hay fever, with tree pollen accounting for roughly one quarter of all cases. Birch pollen poses the primary concern for those sensitive to tree pollen during this period.The Met Office has additionally cautioned that ash pollen concentrations are expected to remain elevated throughout the coming days.Southern England remains the primary hotspot, with forecasters predicting very high birch pollen concentrations across the region for the entire week.London and the South East recorded the most severe levels on Easter Sunday, before the red alert expanded to encompass the whole of southern England on Monday.This includes the South West, West Midlands, East Midlands and eastern England.Hay fever sufferers could be in for a rough week as temperatures are set to rise | GETTYBy Tuesday, nearly every region of England and the entirety of Wales are expected to experience very high birch pollen levels alongside elevated ash pollen.The North East, much of Scotland and Northern Ireland will see high pollen counts on Tuesday, whilst the far north of Scotland should experience more moderate levels.Eight UK areas have been placed under the very high red alert this week.Wednesday will see the most intense conditions concentrated in seven English regions, including London and the South East, the South West, both Midlands regions, eastern England, the North West and Yorkshire and Humber.The Met Office said that the pollen count was expected to be “very high” in most of England and Wales | PAThose impacted by hay fever typically experience intense sneezing, itchy and watery eyes, and throat irritation when pollen counts reach very high levels.The NHS lists additional symptoms including coughing, a runny or blocked nose, and itchiness in the mouth, nose and ears.Hay fever occurs when the immune system produces allergic antibodies in response to pollen particles, triggering the release of histamines that cause these uncomfortable reactions.Allergy UK has issued guidance for those struggling with symptoms during this high-pollen period.The Met Office’s pollen forecast for Tuesday | MET OFFICEThe charity recommends reducing time spent outdoors when pollen counts peak and considering wearing a face covering when venturing outside.Sufferers should also keep windows closed at home to prevent pollen from entering and avoid hanging laundry outside to dry, as clothing can collect pollen particles.Warmer conditions create optimal circumstances for pollen to thrive, intensifying the challenge for allergy sufferers.The surge in pollen coincides with a dramatic shift in weather conditions following Storm Dave, which battered parts of the country over the Easter weekend with gusts reaching 93mph in Wales and leaving thousands of homes without power.Northern regions endured particularly harsh conditions, with snow storms and freezing temperatures affecting many areas.However, warmer air from continental Europe is now moving across the country, bringing a marked change in conditions.Met Office meteorologist Greg Dewhurst said: “On Tuesday, warmer air moves in across England and Wales from the near continent through Tuesday and into Wednesday. “We will see temperatures rising to the low 20s, with highs around 20C or 21C on Tuesday, and possibly 23C or 24C come Wednesday. The sunniest skies on Wednesday may be limited to south-east England, where 23C and 24C is most likely.”Should temperatures reach 23C in southern England on Tuesday, this would exceed the current warmest day of 2026, when Gogerddan near Aberystwyth recorded 20.9C on March 18.