Nasal flaring is when the nostrils widen when you breathe. It is often a sign that is it difficult to breathe.

Flaring of the alae nasi (nostrils); Nostrils - flaring

Nasal flaring is seen mostly in infants and younger children.

Any condition that causes difficulty breathing can cause nasal flaring. While many causes of nasal flaring are not serious, some can be life threatening.

In young infants, nasal flaring can be a very important symptom of respiratory distress.

• Asthma (acute)
• Airway obstruction (any cause)
• Bronchiolitis
• Croup
• Epiglottitis (acute)
• Pneumonia
• Transient tachypnea of the newborn

Seek immediate emergency help if you or your child has signs of a breathing difficulty.

Call your health care provider if:

• There is any persistent, unexplained nasal flaring, especially in a young child.
• Bluish color develops in the lips, nail beds, or skin. This is a sign that breathing difficulty is severe and may mean that an emergency condition is developing.
• You think that your child is having trouble breathing.

The doctor or nurse will perform a physical exam and ask questions about the symptoms and medical history, such:

• When did the symptoms start?
• Are they getting better or worse?
• Is the breathing noisy, or are there wheezing sounds?
• What other symptoms are there, such as sweating or feeling tired? 
• Do the muscles of the stomach, shoulders, or rib cage pull inward during breathing? (See: intercostal retractions)

The doctor or nurse will listen carefully to the breath sounds. This is called auscultation.

Tests that may be done include:

• Arterial blood gas analysis
• Complete blood count (CBC)
• ECG
• Pulse oximetry to measure blood oxygen level
• X-rays of the chest

Oxygen may be given if there is a breathing problem.

Wiebe RA, Scott SM.  General approach to the pediatric patient. In: Marx J, ed. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 7th ed. St. Louis, Mo: Mosby; 2011:chap. 164.