Manufactures are only required to report material if it makes up more then 5 % of the material in the fabric. 5 % is plenty to cause an allergic reaction.
USA http://www.ftc.gov/bcp/edu/pubs/business/textile/bus21.shtm
Australia http://www.accc.gov.au/content/index.phtml/itemId/614083
Canada http://www.cb-bc.gc.ca/eic/site/cb-bc.nsf/eng/01249.html
