What causes asthma?

What causes asthma is different to what triggers asthma:

• The causes are the underlying reasons why someone gets asthma in the first place.
• Triggers are things like dust mites or pollen that can make asthma symptoms worse.

This page talks about the genetic or environmental factors that can make developing asthma more likely, either for a child getting asthma, or an adult getting asthma in later life.

You can read more about asthma triggers here.

The good news is that most people who develop asthma can manage it well.  

You’re more likely to develop asthma if it’s in your close family, such as your parents or brothers and sisters. This is partly down to genetics and partly down to the shared environment you live and grow up in.

If you have asthma yourself, your child is much more likely to have asthma too, particularly if both parents have asthma. There’s slightly more chance of asthma being passed on by the mother than the father.

But having someone with asthma in your close family doesn’t mean you or your child will definitely get it. And people can get asthma without anyone in their family having it.

Children with allergic rhinitis (an itchy or runny nose due to an allergy, like pollen) or eczema, or a family history of allergies, are more likely to develop asthma. Children with a food allergy are said to be four times as likely to have asthma as children without a food allergy.

So, if your child is wheezing or coughing, and they also have a history of allergic rhinitis (such as hay fever), eczema, or a food allergy, it’s much more likely that their symptoms are due to asthma.

Sometimes allergies overlap and sometimes your child will grow out of one allergy and develop another. For example, a small child with eczema may go on to have a food allergy, and then, as they get older, hay fever, and then asthma.

Find out more about how asthma is diagnosed in children.

A child is more at risk of asthma if they were born prematurely (before 37 weeks), especially if they needed a ventilator to help them breathe after the birth.

A low birth weight can also be a risk factor for asthma.

Bronchiolitis

If your child has had a few episodes of bronchiolitis, they could be more at risk of getting asthma as they get older.

Bronchiolitis is caused by a virus, usually the respiratory syncytial virus (RSV). It‘s mostly babies and young children under two years old who get bronchiolitis. It leads to swelling in the lungs and airways, cough, and wheeze.

Your baby is more at risk of bronchiolitis if you smoke.

Croup

Children with a history of croup may also be more at risk of developing asthma. Like asthma, croup has symptoms like coughing and feeling breathless.

Sometimes asthma gets missed because parents think it’s croup. But croup is very rare after the age of five, so if your child is still being treated for croup after this age, your GP should check to see if they have asthma.

Occupational asthma is a type of asthma caused by certain things found in the workplace, such as chemicals or dust from flour or wood.

If you haven’t had asthma before and then get it because of the work you do, and if your symptoms improve when you’re not at work, you probably have occupational asthma. See your GP as soon as possible for advice. If they think there is an occupational cause for your asthma they should refer you to a specialist.

Occupational asthma is a common cause of adult-onset asthma.

Find out more about occupational asthma.

Hormones can play a part in the development of asthma. After puberty more girls than boys get asthma.

And some women first develop late-onset asthma during or after the menopause. Hormones are a common cause for women developing asthma in later life.

Find out more about hormones and asthma.

Research has shown that smoking during pregnancy and smoking around your baby or child, both significantly increase the risk of a child developing asthma or other breathing problems.

And smoking also has a part to play in adult-onset asthma.

The good news is, quitting smoking can really lower your risk of asthma symptoms.

Air pollution, like traffic fumes, can make asthma symptoms worse.

Studies also show that air pollution may play a part in causing asthma too. For example, children living near very busy roads are more likely to develop asthma.

Join our campaign for clean air. 

Being obese or very overweight (having a high Body Mass Index or BMI) increases your risk of asthma attacks.

Research also suggests a link between excessive weight gain in young children and their risk of developing wheeze and asthma.

Putting on excess weight during pregnancy is also thought to increase a child’s risk of getting asthma. And babies born with a high birth weight may have an increased risk of asthma.

For all of us maintaining a healthy weight is important. If you are very overweight, losing weight can improve asthma symptoms.

Some studies suggest a link between very low levels of vitamin D and children with wheeze, allergic rhinitis, and asthma. Good levels of vitamin D during early pregnancy have been found to lower the risk of early wheezing in children.

It’s thought that vitamin D deficiency may be adding to the numbers of people with asthma and other allergies.

Your GP can do a blood test to check your vitamin D levels. If they are low they may suggest supplements.

Find out more about taking vitamin D. 

The widespread use of antibiotics in early childhood and during pregnancy has been linked to an increase in allergies and asthma.

It’s thought that antibiotics may be one of the reasons why there are more people with asthma and allergies.

Antibiotics can be lifesaving, but we can all play a part by making sure we only take antibiotics when necessary. If we do need to take them, it’s important to take them exactly as prescribed. The NHS has more information about using antibiotics safely.

Changes in how we live and work, from more rural to more urban environments, may have a role in causing asthma.

Research suggests that we have less contact with the ‘friendly bacteria’ that thrive in more rural, natural environments. For example, studies show that children growing up on farms, and exposed to ‘friendly bacteria’, are less likely to develop asthma and allergies. This is sometimes called the ‘hygiene hypothesis’.

Nevertheless, “personal and home cleanliness is still important,” says Dr Andy Whittamore, Asthma + Lung UK’s in-house GP.

If you have symptoms like coughing, wheezing, breathlessness, or a tight feeling in your chest, see your GP as soon as possible.

Find out more about how asthma is diagnosed in adults and children.