People are being asked to check on vulnerable neighbours as a heatwave grips much of the UK.
The mercury is expected to peak at 35C later this week as temperatures soar in many areas.
It should start to become very warm and night-time values are not expected to fall below the low-20s C.
Ruth May, chief nursing officer for England, said: "Like lots of people I'm looking forward to having fun in the sun with family and friends, but nobody wants to spend a pleasant day stuck in a hospital or urgent treatment centre.
"It's really important to take simple precautions like drinking plenty of water, using high-factor sunscreen and remembering to take allergy medication if you need it - as is making sure to check in on neighbours and loved ones who can suffer the most from heat and pollen."
People with minor illnesses are urged to check the NHS website or call 111 for help.
Dr Andy Whittamore, clinical lead at Asthma UK and a practising GP, said: "A toxic cocktail of hot humid weather and rising pollen levels this week could be extremely hazardous for the 5.4 million people in the UK with asthma, triggering deadly asthma attacks.
"Hot air and hay fever can cause people's airways to narrow, leaving them struggling to breathe, with symptoms like coughing, wheezing, a tight chest and breathlessness.
"Hot weather can also increase the amount of pollutants, pollen and mould in the air which can trigger asthma symptoms.
"If you are worried about the weather or hay fever affecting your asthma, make sure you take your hay fever medicines, keep taking your regular preventer as prescribed by your doctor and carry your blue reliever inhaler at all times."
The Met Office has warned that the sweltering spell could bring some disruption from heavy thundery downpours.
This could lead to some localised flooding and travel disruption, according to the Met Office.
"As we head through the week, the rain will generally begin to ease across northern areas, so the potential is for much of the UK to see some hot conditions," the Met Office spokesman said.
"There will be some sunshine around during the week, but also the risk of some heavy thundery downpours as well."
Temperatures will increase as the week progresses, according to forecasters, reaching highs of 33C (91F) on Tuesday, 34C (93F) on Wednesday and 35C (95C) on Thursday.
Although the main concentration of the hot weather will be in central and south-eastern England, parts of Scotland could reach the high 20s.
For the majority of the UK, the mercury needs to hit 25C for three consecutive days to be classed as a heatwave.
This threshold increases the further south east in the country, with temperatures in London needing to reach 27C.
The maximum temperature recorded in July is 36.7C (98F), on the first day of the month in 2015 at Heathrow.
Looking ahead to next weekend, the Met Office expects temperatures to fall.
"It looks most likely that, at least by Saturday, most areas will see a bit of a drop in temperatures," the forecaster said.
