Buddhism holds that physical suffering and misfortune all have various contributing factors as their causes. Some illnesses, the so-called karma-induced illnesses, originate from previous lives. They are medically incurable, no matter how much money is spent. These may be attributed to karma. If you have a cold, headache, or fever, this may also be karma-related, but not necessarily caused by karma from past lives. Hence, karma is sometimes directly responsible for certain occurrences, but other times may not be so directly involved. The point is, in all matters, Buddhism has always opposed taking a dualistic approach, affirming one side while negating the other. The same applies to karma.

~ Luminous Wisdom Book Series 1: On Cause and Effect