Hot weather, thunderstorms and high pollen can combine to trigger breathing problems. This is what you need to know, even if you've never had asthma before.
Warm, muggy days, high pollen and rumbling thunder are all familiar features of a British summer. But occasionally that combination can trigger a sudden surge in wheezing and breathlessness known as thunderstorm asthma.
UKHSA’s Adverse Weather and Health Plan for England was updated in April 2026 to include thunderstorm asthma as an “additional hazard”.
The move comes amid growing evidence of the risk. June 2023 saw the largest thunderstorm-asthma episode in England since the national health monitoring system began more than 25 years ago.
“More than seven million people in the UK are living with asthma,” says Karen Spillett, deputy head of health advice at Asthma + Lung UK. “People with asthma can experience severe symptoms due to thunder, especially when pollen is high.”
Thunderstorm asthma is the name given to asthma symptoms or attacks triggered by conditions around some thunderstorms.
“It’s thought this is because the atmospheric conditions break the pollen down into tiny particles that bypass the body’s defences and go deeper into the lungs,” says Spillett.
Storm winds carry these fragments towards ground level. The risk is greatest after warm, humid weather when grass pollen or fungal-spore levels are high.
UKHSA says people under 30 appear more likely to be affected. The June 2023 increase in England was seen among people aged five to 64, while no overall rise was detected in the under-fives or over-65s.
Greater outdoor exposure may help explain why young people and adults of working age appear more susceptible, says Dr Sarah Diver, senior clinical research fellow at the University of Leicester and an honorary respiratory consultant.
The figures don’t mean that other groups are immune. “Thunderstorm asthma can affect people of any age,” says Dr Matt Swallow, GP and clinical lead at Asthma + Lung UK. Anyone with asthma, undiagnosed asthma or hay fever can suffer from it.
Allergy UK advises keeping asthma and hay fever well controlled. Poorly controlled hay fever can exacerbate asthma symptoms.
“Some people who experience thunderstorm asthma have hay fever but no previous diagnosis of asthma,” says Dr Swallow. For some, it may be their first noticeable asthma attack.
During Leicester’s June 2023 episode, there were 149 asthma-related A&E presentations over two days – 6.6 times the three-year average – and 29 adults were admitted to hospital.
“A lot of the patients didn’t know they had asthma or felt they had mild asthma,” says Dr Diver, who was working in the hospital that night. Many weren’t using inhalers regularly or were receiving little treatment. They generally responded well to standard asthma care.
One episode doesn’t necessarily mean you have developed chronic asthma, adds Dr Swallow, but you should arrange a medical assessment to check for underlying asthma or another cause.
Thunderstorm asthma can be life-threatening, although severe outbreaks are rare. “Hay fever can cause asthma symptoms to worsen and thunderstorm conditions can cause even mild symptoms to become severe, such as difficulty breathing and chest tightening,” says Amena Warner, head of clinical services at Allergy UK.
“Anyone who experiences difficulty breathing should seek medical help without delay.”
The world’s largest recorded outbreak struck Melbourne in November 2016: thousands needed medical help and 10 people died.
Thunderstorm asthma specifically refers to asthma, but high pollen and airborne particles may aggravate COPD, says Dr Swallow. Older people with lung or heart disease may face more serious consequences from acute breathlessness.
New or worsening breathlessness should be medically assessed; seek urgent help if it’s severe or rapidly intensifying.
Possibly, although heat alone isn’t responsible and there is no clear pattern of increasing summer thunderstorms, says Dr Diver.
Rising temperatures are linked to earlier and longer allergen seasons, potentially widening the period in which outbreaks could occur.
Dr Diver led a 2025 analysis of the Leicester episode that identified Cladosporium fungal spores as a possible factor. “They’re a lot smaller than pollen particles, so they can travel further down into the lungs and cause a problem,” she says.
UKHSA has also linked rising carbon dioxide levels with increased atmospheric pollen and spores from some allergenic fungi.
Asthma + Lung UK advises contacting your GP if your usual treatment isn’t helping or you need your inhaler more often.
Sit upright, remain calm and don’t lie flat, says Dr Swallow. Use your reliever inhaler as directed in your action plan. Call 999 if your symptoms worsen, the maximum dose stated in your action plan doesn’t help or you don’t have an inhaler. Don’t drive to A&E.
If you’re experiencing a possible first attack, call 999 for severe breathlessness, difficulty speaking, exhaustion, confusion, blue lips or fingers, or rapidly worsening symptoms, says Dr Swallow.
Even if you recover, see a GP within two days, suggests the NHS.
“Thunderstorm asthma remains relatively uncommon in the UK,” says Dr Swallow. “Most people with asthma will never experience it.”
Mike Scott, 56, has had asthma since childhood. About 20 years ago, after more than a year without symptoms, he travelled to Norwich without an inhaler. A thunderstorm arrived after a hot, humid day. “My chest started getting tighter and tighter,” he says.
Mike drove himself to A&E – something the NHS advises against: “I thought they’d give me a few puffs of Ventolin [a reliever inhaler] and I’d be on my way. But they put me on oxygen for three or four hours.”
A nurse told him that 26 of the 27 patients there that night had asthma-related problems. Mike returned to prescribed inhalers and hasn’t had another serious attack. “If I was going away, I would definitely take an inhaler,” he says.
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