To review and evaluate the evidence for the widespread view that signs and symptoms of rheumatoid arthritis (RA) are influenced, or even caused, by the weather.
A literature search from 1985 to April 2003 was performed using the PubMed database of the US National Library of Medicine. Additional relevant articles were identified from the bibliographies, and from our own archives. Methods and findings of the studies were critically reviewed.
Only temperature and humidity appear to have clear influences on the symptoms of RA, although the reported findings do not agree. In many cases, the apparent controversies can be explained by the intimate relationship between temperature and humidity, and by taking local circumstances into account. The differences in the methods applied in studies on effects of weather on RA strongly hampered our evaluation.
RA variables are positively correlated with the humidity of the microclimate at the patient's skin. High outdoor relative humidity is unfavorable, but has less influence when there are few barriers for water vapor, like clothes, and when air conditioning is used. High temperature is unfavorable since it increases absolute humidity, but beneficial as well, since it reduces the presence of barriers, and stimulates the use of air conditioning. The classic opinion, "Cold and wet is bad, warm and dry is good for RA patients," seems to be true only as far as humidity is concerned.