Croup is an infection that causes the voice box and the windpipe to swell. It is characterized by a barking, hacking cough and can lead to difficulty breathing. Croup is diagnosed in up to 5% of children younger than age six, 1% of whom are hospitalized. Providing humidity or mist for a child to breathe is often used by both parents and hospitals to relieve symptoms.

Humidity is thought to soothe the inflamed tissue and loosen and thin the mucus. It can be administered via steam from a shower or kettle at home or by blow-by technique, croup tents, or face masks in a hospital setting. Using humidity does have some drawbacks, such as croup tents frightening a young child, which can worsen airway obstruction, or aerosolized water droplets causing hot water scalds. Additionally, clinical trials that have looked at its effectiveness have had mixed results. A study published in the March 15, 2006 issue of the Journal of the American Medical Association evaluated whether different types of humidity improved symptoms of croup in children.

About the Study

The study included 140 children (average age 25 months) who arrived at a Toronto hospital emergency department with croup. The children were randomly assigned to receive one of three treatments:

  • Blow-by humidity for 30 minutes (mist therapy – delivered via a plastic tube held by the parent and directed at the patient’s face from a distance of 20 centimeters)
  • 40% humidity (low humidity – delivered via tubing and face mask)
  • 100% humidity and microscopic water droplets (high humidity – delivered via tubing and face mask)

The primary outcome of the study was a change in the croup score, which is used to measure symptom severity.

After treatment, there was no difference in outcomes among the high humidity, low humidity, and mist therapy groups. The differences at 30 minutes and at 60 minutes were minimal and not clinically or statistically significant. Additionally, none of the children worsened during the study period.

This study does have limitations, including not having a control group. A control group is randomized to receive a placebo or no treatment, allowing investigators to better analyze the effect of the treatment being studied. But, treatment cannot be withheld from a child. The authors suggest that the blow-by technique should be considered the placebo for this study, because it is essentially equivalent to breathing the surrounding room air.

How Does This Affect You?

When you hear that barking cough and sense that your child is uncomfortable, you naturally want to do anything that will help. For years, parents and clinicians alike have used humidity for this purpose. Do these study results suggest that your child should no longer be treated in this way? The authors suggest that humidity may be useful because of the other factors associated with it, like the comfort of being close to parents or the soothing temperature used for its delivery.

In this study, more than one-third of mild croup cases resolved within 30 minutes without treatment. If you do decide to provide mist or humidity for your child at home, stay with your child to help him or her feel safe and comfortable. If you use hot water to create the steam, be careful to protect your child from the risk of being burned.