When Nasal cannula oxygen should be humidified?

When the flow rate is greater than 4 L/min.

Humidification is recommended for nasal cannula oxygen when given at flow rates higher than 4 liters/minute. This is because the dry oxygen can cause drying and irritation of the nasal passages, which can lead to discomfort and potential damage to the nasal mucosa. Humidification helps to add moisture to the oxygen, which can help to prevent these problems.