The association with environmental factors was seen in a US study which looked at external climate conditions and eczema data for over 91,000 children aged from 0 to 17 years. The factors most associated with an increased likelihood of eczema in children were:8

·       low annual relative humidity

·       low mean annual UV levels

·       low mean annual temperatures

·       the more days where temperatures were below 18°C (65°F) (possibly due to decreased indoor humidity because of having the heating on)

·       increased rain levels/days of precipitation (possibly due to reduced UV exposure because of cloud cover, and more time spent indoors in heated conditions).

However, the seasonal impact is not always clear cut. Another US study looking at long-term dermatology data in relation to climatological regions in the country found that while there is a possibility of seasonal variation in atopic dermatitis, there was no clear evidence of a winter flare of the condition.9

Indeed, the researchers concluded that increased temperature increases the likelihood of a consultation. In the hotter south of the country, there were substantially more visits to primary care physicians for atopic dermatitis in the summer. In the rest of the US, the season with the most visits for atopic dermatitis were the spring.