1

Parental smoking and exposure to wood smoke

2.

Upper respiratory tract infections (rhinitis, nasopharyngitis).

3

Day care attendance

4

Familial tendency

5

Short duration of breastfeeding and bottle feeding.

6

Use of pacifiers and presence of digit sucking

7

Overcrowding

8

Measles, pertussis, tuberculosis and immunosuppression

9

Cleft palate, Down syndrome and other craniofacial defects.