Despite the new discoveries of the Renaissance, explanations of what caused and cured disease had barely changed from the Middle Ages. People still believed:

Disease was sent by God;
Illness was caused by the humours being out of balance;
Miasma - bad air - spread disease;

By the 1700s doctors were less likely to believe in astrology. Some were starting to challenge the Theory of the Four Humours as they began to understand that there was a link between poor living conditions and disease. This was shown by the Bills of Mortality that were collected during the Great Plague. This helped to undermine belief in the four humours as clearly there were environmental factors to disease.

GCSE Health and the People AQA

Renaissance Explanations