Medics have issued an urgent warning as one million people have been left at risk because they are using the wrong asthma medication.
Research by Asthma + Lung UK fear many are using an incorrect inhaler - and it could have deadly consequences.
The charity say one in five conditions are being incorrectly controlled as the alarm was raised ahead of more sweltering heat this week.
They want "outdated" national guidance on asthma care to be updated.
Sufferers are usually given two types of inhaler, a blue reliever to help ease symptoms like coughs and wheezes. The brown inhaler helps tackle inflammation, offering protection against asthma attacks.
New research has revealed a fifth of asthmatics are using the 'reliever inhaler at least three times too much'.
Clinical Lead at Asthma + Lung UK Dr Andy Whittamore has sparked concerns and urged patients to book GP appointments.
The practising GP told The Sun : “It’s vital that people with asthma have access to a preventer inhaler and take it every day, as this keeps the inflammation down in your airways and prevents symptoms.
"You should still take your reliever inhaler when symptoms come on.
"But if you are needing it three times a week or more, this is a sign of untreated inflammation in your airways and it's really important you make an appointment with your GP, nurse or pharmacist to discuss your treatment options."
The problem can trigger breathing difficulties, leading to potentially fatal attacks.
Sarah Woolnough, chief executive of Asthma and Lung UK, says no lives should be needlessly cut short.
She said people with asthma are being let down by "dismal rates of basic care caused by pressures on the NHS and outdated treatment guidelines".
The chief executive said that four people still die of an asthma attack every day but said deaths from asthma are often preventable.
"We don't want to see any more lives needlessly cut short," she added.
