The number of hayfever sufferers in the UK is predicted to reach 20 million this summer, up a third from last year as warm weather bathes the country. For many, the glorious sunshine and promise of temperatures warmer than the Mediterranean this week will come as a welcome relief. But for millions, the  first tentative steps towards summer brings impending misery as a dreaded cloud of invisible pollen descends. Experts told MailOnline that five million people are expected to fall victim to the symptoms  - which include streaming eyes, incessant sneezing and irritating itches at the back of the throat - for the first time. Around 20 million people in the UK are expected to suffer hayfever symptoms this summer, up a third from last year, experts told MailOnline . And by 2030 that figure is expected to surge to 31.8 million sufferers. Dr Jean Emberlin, a leading pollen expert, told MailOnline that a 33 per cent rise in the number of people struck by hayfever this year could occur, 'depending on weather conditions'. She said: 'If we get prolonged periods of warm, dry weather with intervals of some wet weather between, which helps the grass to keep growing, we will experience a lot of high grass pollen counts. 'Grass is the main culprit pollen for hayfever in the UK. 'High and very high pollen counts can trigger hayfever symptoms in people who have not had them before. She added: 'In addition, the good weather typically brings increases in air pollution, which can make symptoms worse, and again lead them to occur in people who have been symptom free before.' In addition, she said pollen is becoming more potent, and greater numbers of plants giving off the allergens is also contributing to a rising number of sufferers. Dr Emberlin said another contributing factor is that the average hayfever season is becoming longer, typically stretching from April to the end of August. She added: 'There is substantial evidence from pollen monitoring records and from vegetation surveys to show that the timing of some of the pollen seasons has been changing in the UK and across Europe over the last few decades. Hayfever seasons in the UK are becoming longer, as warmer weather in spring and autumn means pollen is typically rife from March to the end of August . 'In addition there has been a trend to longer pollen seasons and increasing pollen loads of some types. 'Globally, average surface temperatures have increased by about 0.7°C over the past 100 years, leading to earlier plant growth in many regions. 'The trend towards warming has been more pronounced in winter months, resulting in more changes in the timing of spring pollen seasons than those of summer and autumn.' Hayfever is an allergic reaction to pollen and spores. It happens when the immune system mistakes these harmless airborne particles to be a danger and launches a defence against them. The body produces an antibody and histamine is released which causes the typical symptoms of sneezing, runny nose and eyes, an itching nose and mouth, and possibly a blocked nose. The allergy is a seasonal one, triggered by a range of different pollens ranging from tree to grass, weeds to fungal spores. By 2030, Dr Emberlin predicts there will be 31.8 million sufferers as the situation will worsen. 'As summers become warmer more photochemical smogs will occur on dry days resulting in an increased frequency of days with high concentrations of ozone, NOx and other pollutants that will make symptoms worse, and that will make people more susceptible to allergens,' she said. 'Due to climate change in the future, plant growth may be influenced in a way that more, new and altered pollens are produced, which may affect humans.' Dr Emberlin, speaking on behalf of Opticrom Hayfever Eye Drops, warned the season is expected to start suddenly with pollen counts surging from almost nothing to very high in a matter of days. Friday is set to be the hottest day of the year so far, with the mercury poised to rise steadily to reach 21°C in parts of southern England. In preparation, hayfever sufferers are being encouraged to take action, stocking up on antihistamines and other treatments to lessen the impact of their symptoms. 'It is very important to know the seasons, when it is likely to peak and the days when pollen levels will be particularly high. 'Knowing when the season is about to start means there is lots a person can do. 'If you are not sure of the best treatment you can speak to your pharmacist or GP. 'Steroids are often used to treat hayfever, but they are best taken before the onset of symptoms. Dr Jean Emberlin said: High and very high pollen (pictured under the microscope) counts can trigger hayfever symptoms in people who have not had them before' 'Antihistamines are also commonly used and it is a good idea to get them in and ready to use when the season starts. 'If you have got a big event, like exams or a wedding coming up you can ask your GP to prescribe a short course of steroid tablets to keep symptoms at bay. 'There are lots of options available, the key is just to be organised and ensure you are prepared. 'On days you know the pollen count is high make sure you take antihistamines before you leave the house, and wear sunglasses to keep pollen out of your eyes. 'Make sure you wash your clothes regularly and don't sleep with the window open.' Dr Emberlin said pollen counts can suddenly surge if conditions are right. 'A warm day with a slight breeze can signal the perfect conditions for spores to infest the air, causing pollen levels to surge,' she warned.
Last year 15 million people fell victim to the symptoms of hayfever.
This year that number is expected to rise by a third to 20 million.
Experts told MailOnline warmer weather can result in very high pollen counts which trigger symptoms in new sufferers.
High temperatures also increase air pollution, which worsen symptoms.