Calls to an asthma helpline have surged by more than 40% as high pollen levels leave people struggling to cope.
The sizzling heatwave, forecast to continue, has been accompanied by high pollen levels, which put asthma sufferers at risk of a "life-threatening" attack.
The Asthma UK helpline received 642 calls in June, up from 450 in April - a 42.7% increase - with the charity pointing out that pollen count is a factor.
Sonia Munde, head of services at Asthma UK, said: "Calls to Asthma UK's specialist nurse-staffed helpline surged by over 40% in June, with many callers saying that they are struggling to cope with high pollen levels affecting their asthma.
"An estimated 3.3 million people in the UK who have asthma say their pollen allergy triggers their asthma so as well as having to deal with hayfever symptoms such as itchy eyes, sneezing and a running nose, they're also at risk of a life-threatening asthma attack.
"People who have asthma and a pollen allergy should take hayfever medicines, such as antihistamines and nasal steroid sprays, and make sure they take their preventer inhaler as prescribed for the best chance of staying well."
Temperatures are forecast to remain in the mid to high 20s - as hot as holiday destinations Barcelona and Tenerife.
The UK basked in one of its hottest and driest Junes ever, and the weather is not changing any time soon, although there is a risk of showers in southern parts.
Met Office forecaster Bonnie Diamond said the warm weather is "certainly lasting through this week".
"There's a signal that it will continue into next week as well, with many places staying dry, sunny, very warm and light winds.
"Over the weekend especially, across southern parts of the UK, it will turn hot, possibly seeing a return to temperatures into the low 30s."
Asked about temperatures in European hot spots, Ms Diamond said: "It's going to be as hot as Barcelona and Tenerife."
The mercury will hit 28C-29C in Barcelona this week, with 30C possible on Saturday.
"That's not out of the question for parts of the south into the weekend," Ms Diamond added.
Cancer Research UK has urged people to protect their skin, with spokeswoman Fiona Osgun saying: "Tanning isn't a sign of good health - it's a sign that your skin is trying to repair the damage UV has caused in your cells.
"And getting a sunburn just once every two years can triple the risk of melanoma, so don't let sunburn catch you out."
Dr Bav Shergill, of the British Association of Dermatologists, urged people to use common sense and wear sunscreen, adding: "Don't forget your ears, don't forget your chest, and your other exposed surfaces.
"It's bright enough at 9 o'clock in the morning, to be honest with you, at the moment. It's so bright. I would definitely advocate wearing sun cream before you get out of the house.
"We're not used to it in this country. In Australia they're a not more switched on to wearing sun cream all the time. It's part of the culture."
Bookmaker Ladbrokes slashed the odds to 5/4 that the heatwave lasts until August.
It is odds-on at 4/6 that the mercury goes past 35C this week.