What could cause high IgE levels?

Genetics. The tendency to make more ige in response to foreign substances that enter the body (aka allergens) is inherited. Allergies and parastic infections are the common reasons why people develop high ige levels. There are some rare disorders associated with increased risk of infections associated with very high levels of ige. A board-certified allergist can help sort this out for you.
Allergies. An elevated ige is usually associated with allergies. There are other rare conditions that may cause ige to be extrememly elevated.