Baseline characteristics
| Exposed | Unexposed | |
| Number of patients (n) | 2 491 086 | 3 120 719 |
| Number of patients with asthma diagnosis (n) | 472 984 | 289 969 |
| Number of patients with eczema diagnosis (n) | 455 348 | 367 786 |
| Median (IQR) follow-up period (person years) | 5.10 (2.02–9.68) | 4.11 (1.59–8.37) |
| Mean (SD) age at cohort entry (years) | 39.42 (23.65) | 35.81 (22.17) |
| Sex (n) | ||
| Male | 1 129 954 | 1 561 074 |
| Female | 1 361 132 | 1 559 645 |
| Body mass index, n (%) | ||
| Underweight (<18.5 kg/m2) | 40 490 (1.63) | 52 235 (1.67) |
| Normal (18.5–24.9 kg/m2) | 687 723 (27.61) | 823 574 (26.39) |
| Overweight (25.0–29.9 kg/m2) | 541 784 (21.75) | 559 329 (17.92) |
| Obese (>30.0 kg/m2) | 348 395 (13.99) | 310 123 (9.94) |
| Not available | 872 694 (35.03) | 1 375 458 (44.08) |
| Smoking status, n (%) | ||
| Current smoker | 348 532 (13.99) | 474 771 (15.21) |
| Non-current smoker | 1 574 697 (63.21) | 1 681 583 (53.88) |
| Not available | 567 857 (22.80) | 964 365 (30.90) |
| Drinking status, n (%) | ||
| Current Drinker | 1 266 898 (50.86) | 1 394 975 (44.70) |
| Non-current drinker | 370 169 (14.86) | 382 726 (12.26) |
| Not available | 854 019 (34.28) | 1 343 018 (43.04) |
| Townsend index, n (%) | ||
| (Least deprived) 1 | 535 228 (21.49) | 657 580 (21.07) |
| 2 | 464 489 (18.65) | 552 877 (17.72) |
| 3 | 453 156 (18.19) | 559 350 (17.92) |
| 4 | 388 862 (15.61) | 487 367 (15.62) |
| 5 | 262 946 (10.56) | 327 038 (10.48) |
| Not available | 386 405 (15.51) | 536 507 (17.19) |
| Ethnicity, n (%) | ||
| White | 1 050 939 (42.19) | 1 114 783 (35.72) |
| Black | 45 742 (1.84) | 51 975 (1.67) |
| South Asian | 66 060 (2.65) | 74 028 (2.37) |
| Mixed | 16 818 (0.68) | 19 858 (0.64) |
| Other | 37 641 (1.51) | 54 616 (1.75) |
| Missing | 1 273 886 (51.14) | 1 805 459 (57.85) |