Research...
General Reference
Wikipedia: Food Allergies
This is a broad topic and the article is extensive. Be sure to click on appropriate links and check out the "ideal sources" suggested on the "talk" tab.
Consumer Medical Resources
WebMD | MayoClinic.com | Healthline | Sharecare
Periodical Databases
AltHealthWatch | Consumer Health Complete | Health Source | Medline
The Open Web
For each site you find ask yourself:
Is this a personal blog? a forum?
Who sponsored/authored this site and what professional credentials do they lend to the site?
Is the site selling some product or idea? Does this effect the message (expected bias)?