The exact cause of Churg-Strauss syndrome is unknown. It's likely that an overactive immune system response is triggered by a combination of genes and an environmental trigger, such as allergens or certain medications. Instead of simply protecting against invading organisms such as bacteria and viruses, the immune system overreacts and targets healthy tissue, causing widespread inflammation.

Some people have developed Churg-Strauss syndrome after using an asthma and allergy medication called montelukast or after switching from low-dose oral systemic steroids to inhaled steroid medications. However, no clear connection between Churg-Strauss syndrome and any medication has been proved.

Jul. 12, 2013