Association between combinations of smoking by the parents and symptoms of asthma, eczema and rhinoconjunctivitis at 6–7 and 13–14 years of age
| Symptom | Mother only smokes | Father only smokes | Mother and father smoke | RERI |
| 6–7 years | ||||
| Current wheeze | 1.31 (1.22 to 1.41) | 1.13 (1.08 to 1.18) | 1.37 (1.29 to 1.45) | −0.071 (−0.182 to 0.040) |
| Severe asthma symptoms | 1.31 (1.18 to 1.46) | 1.19 (1.11 to 1.27) | 1.46 (1.34 to 1.59) | −0.042 (−0.205 to 0.121) |
| Asthma ever | 1.28 (1.19 to 1.38) | 1.07 (1.02 to 1.12) | 1.29 (1.22 to 1.38) | −0.057 (−0.168 to 0.054) |
| Current eczema symptoms | 1.15 (1.06 to 1.24) | 1.07 (1.02 to 1.12) | 1.19 (1.11 to 1.27) | −0.029 (−0.136 to 0.078) |
| Current rhinoconjunctivitis symptoms | 1.13 (1.04 to 1.23) | 1.07 (1.02 to 1.12) | 1.16 (1.09 to 1.24) | −0.035 (−0.141 to 0.070) |
| Eczema symptoms without wheeze | 1.06 (0.97 to 1.16) | 1.03 (0.98 to 1.09) | 1.13 (1.05 to 1.22) | 0.040 (−0.075 to 0.155) |
| Rhinoconjunctivitis symptoms without wheeze | 1.08 (0.98 to 1.19) | 1.04 (0.98 to 1.09) | 1.06 (0.98 to 1.15) | −0.052 (−0.173 to 0.069) |
| 13–14 years | ||||
| Current wheeze | 1.27 (1.19 to 1.36) | 1.13 (1.07 to 1.18) | 1.43 (1.36 to 1.51) | 0.040 (−0.066 to 0.146) |
| Current wheeze (video) | 1.38 (1.25 to 1.52) | 1.17 (1.10 to 1.25) | 1.50 (1.39 to 1.63) | −0.046 (−0.203 to 0.111) |
| Severe asthma symptoms | 1.28 (1.18 to 1.39) | 1.16 (1.09 to 1.23) | 1.57 (1.47 to 1.67) | 0.128 (−0.004 to 0.260) |
| Asthma ever | 1.16 (1.09 to 1.23) | 1.04 (0.99 to 1.08) | 1.21 (1.16 to 1.28) | 0.021 (−0.064 to 0.107) |
| Current eczema symptoms | 1.20 (1.10 to 1.30) | 1.17 (1.10 to 1.23) | 1.33 (1.24 to 1.42) | −0.040 (−0.160 to 0.080) |
| Current rhinoconjunctivitis symptoms | 1.15 (1.08 to 1.23) | 1.12 (1.07 to 1.17) | 1.27 (1.21 to 1.34) | 0.000 (−0.092 to 0.093) |
| Eczema symptoms without wheeze | 1.16 (1.06 to 1.27) | 1.16 (1.10 to 1.23) | 1.18 (1.10 to 1.27) | −0.139 (−0.266 to −0.012) |
| Rhinoconjunctivitis symptoms without wheeze | 1.06 (0.99 to 1.13) | 1.10 (1.05 to 1.15) | 1.18 (1.11 to 1.25) | 0.022 (−0.068 to 0.113) |
Data are OR (95% CI) and are adjusted for gender, language, region and GNI category. Reference group is neither parent smokes.
RERI, relative excess risk due to interaction between the two smoking exposures.