If yo uare using a shampoo for yoru hair that has selenium in it, it could remove the mercury from your hair. I have read somewhere that Selenium is used to get mercury out of your body, so maybe when it is in shampoo it could remove it from your hair. Selenium is in Head and Shoudlers and is used to get rid of dandruff in your hair. So if you have been using a shampoo with Selenium in it, it could have effected the hair test.