Asthma, Reactive Airway Disease, Bronchiolitis and Croup - what are they and how are they different?

By Dr Megan Yap - PaediatricianGeneral10 Aug 2017

I thought I’d do a (hopefully) quick and timely post about asthma, bronchiolitis and croup this morning as I know we are heading into the time of year when there is so much of it around.

This post was inspired by a friend of mine whose little one has had a recent worsening of her asthma in the context of having a cold.  She messaged me last night and said, “Megs, the doctor said that the bouts of asthma [when she is sick with other things] are a reaction to a virus or something.  Is this a thing?”  

Yup – it totes is a thing.

Another very good friend of mine’s little girl recently ended up in emergency at 10pm at night because of croup.

It can get confusing trying to understand the differences in these respiratory illnesses as they are similar in some ways, but different in others – and ALL of them are common.  I will try to explain as clearly and simply as I can.


Asthma, by definition is a CHRONIC (ie you have to have it for a long time) condition of the lungs that causes difficulty breathing and wheezing (a musical sound when you breathe).  The wheezing sound is caused by constriction of your airways (mostly your bronchi and your bronchioles – the small tubes that carry air down into your lungs) and the movement of air through them.  People (or children) who have it, but not yet for a “long time” don’t call it asthma – because it isn’t yet chronic.  Instead, it is called “reactive airways disease” – which is actually kind of a better name for it as it makes sense and describes what is happening.  They are ESSENTIALLY the same disease.

The narrowing of the airway is usually caused by some type of trigger (which is different for different people – for example: cold air, exercise, pollens, a virus or bacteria) that cause the smooth muscle in the walls of your airways to react and constrict.   So you can get “infective” exacerbations of your asthma, or “allergic” exacerbations or even “exercise-induced” asthma.

The airway narrowing is REVERSIBLE by using an inhaled medication called salbutamol (also known as “Ventolin” or “Asmol”) – that binds to a receptor on the smooth muscle and causes it to relax – opening up the airways.


Bronchiolitis is also a respiratory illness in children – caused by a chest infection.  It causes inflammation of the LOWER airways (or specifically, the bronchioles).  The infection is usually some sort of virus (for example Respiratory Syncytial Virus (RSV), influenza).  It usually causes a flu-like illness that affects INFANTS in the first year of life.

Usually the illness starts as a cold – the baby often has a runny nose, they start to cough and then they breathe quickly and develop a wheeze.  They can sometimes have a fever as well.  The breathing difficulties can lead to poor oral intake and troubles with feeding (and then consequently dehydration).  Sometimes these children need to be admitted to hospital for breathing support, or rehydration. Smaller volumes feeds more frequently can help, as can simple pain relief measures like children’s paracetamol (eg Panadol) or ibuprofen (eg Nurofen) If your child has pain (eg a sore throat) or is miserable with a high fever.

Mostly, the symptoms start with the runny nose and cough on the first 1-2 days.  Babies are often sickest on the 2nd-3rd days and will usually start looking better on the 4th or 5th day.  They are often sick for about 7-10 days.  The cough can persist for up to 4 weeks or more.

We do not usually order blood tests OR chest X-rays for bronchiolitis (unless the child looks very ill – in which case it helps us to distinguish the illness from other diagnoses, eg pneumonia).  Medicines are no usually helpful either –

  • Antibiotics do not work to kill viruses so they are not given in bronchiolitis,
  • Salbutamol (ie Ventolin) is not usually helpful as the airway wheezing is NOT reversible like in asthma
  • Steroids do not help to change the course of disease

You should seek medical attention if your child is looking like it is having trouble breathing or looking exhausted, if it has poor oral intake and reduced wet nappies (urine output) that might indicate dehydration.

Doctors (GPs and emergency doctors) are used to seeing lots of babies/children with respiratory illnesses during winter – no one will get cross at you for seeking medical attention if you are worried about the health of your child! 


Croup is a respiratory condition that causes swelling of the UPPER airways – the voice box (or larynx) and windpipe (trachea).  Like bronchiolitis, it is caused by a viral infection and often begins like a normal cold but is characterised by a harsh, barking cough.  Often it is worse at night time, when the temperature drops and the air is colder.

Typically it affects children up until the age of 5 (but I have seen in some kids up to about age 8 – it can persist in older kids particularly if they are born with an airway that is narrower or floppier than normal).  Some kids might only get croup once, whereas other children can have it recurrently.  It can sometimes be mild, but can also get worse very quickly.  If you think your child is having troubles breathing, they should get medical attention immediately.

The illness often starts like a cold (eg runny nose and cough), but then the cough will change in sound and harsh – like a dog or a seal barking.  Your child’s voice might also sound hoarse (laryngitis).  If the upper airway narrowing/inflammation is severe enough, the child might have a high pitched noise on breathing in called a “stridor”  which can get worse if they get distressed.  Croup can last for 1-4 days and the symptoms often worsen at night (being at their worst on the 2nd or 3rd night of the illness).

When should you seek medical attention?

  • If your child has a stridor (the sharp noise when breathing in) when at rest
  • If the muscles between their ribs, suck in when they are breathing (or they look like they are struggling to breathe)
  • If your child is very distressed

Treatment:  Sometimes steroids (eg prednisolone or dexamethasone) are given orally for croup – usually as a single dose.  this reduces the inflammation of the airway to make breathing easier.  Antibiotics do not work to kill viruses, so they are not given in croup.  Keeping your child as calm as possible helps (eg read a book or watch a video), and if they are miserable/irritable with a fever, children’s paracetamol (eg Panadol) or ibuprofen (eg Nurofen) can help.

Wow.  This is actually a much longer post than I intended it to be – whoops.

I hope you have found the information helpful and that YOUR kids (and you) avoid the dreaded lurgy this winter!!!!

Until next time – stay well!

xx Dr Megs

For more from Dr Megan Yap visit her blog – Kids Health Guru


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