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Allergy sufferers are warned of an explosion of pollen across the whole of France.

And the early burst of summery weather this week is only set to make things worse for those susceptible to high pollen counts, the Réseau national de surveillance aérobiologique (RNSA) warned as it issued a red alert across a large swathe of the northern half of the country.

The RNSA said that birch pollen was the main cause of allergies in the north, while plane pollen was on the rise in the south.

"The risk of allergy will be very high in the coming days for birch pollens north of a Bordeaux-Lyon line and in the Alps," the watchdog said.

It added that sufferers could protect themselves by following a few simple measures, including washing their hair in the evening to rid it of pollen, avoid drying clothes outside on high-pollen days, and not opening car windows while driving.