Should I wash my hair before the test?

Air pollution and hair treatments can deposit the desired substances on the outer surface of the hair. Washing the analysed hair strand with suitable solvents removes much of this contamination. 

It remains unclear whether washing the hair completely removes the external contamination on the one hand, and whether it does not start the extraction of the substances embedded in the hair structure on the other. 

Whether the hair is washed or not, any trace of pollution present inside or outside the hair indicates exposure to that pollution. Washing the hair before analysis is necessary to assess the amount that has been incorporated into the hair structure and is directly proportional to the dose to which the body has been exposed.