You may want to know that Bigen is mostly pure PPD (para-phenylenediamine) and contains more PPD than what is allowed according to FDA recommendations (why it's still sold in the US is beyond my comprehension).
Allergic contact dermatitis from para-phenylenediamine in Bigen® powder hair dye.
Ho, S. G. Y.; White, I. R.; Rycroft, R. J. G.; McFadden, J. P.. Contact Dermatitis, Aug2004, Vol. 51 Issue 2, p93, 2p; DOI: 10.1111/j.0105-1873.2004.0396f.x; (AN 14418458)
Bigen Hair dye has a 12.5% PPD content, and may cause severe allergic reactions. 6% is the maximum allowed by FDA law. According to the article above, Dose–time relationships for elicitation of contact allergy to para - phenylenediamine., .01% is sufficient to cause an allergic reaction. quote taken from this page
http://www.hennaforhair.com/ppd/ppdreaction/medarticles.html
For more info on PPD and potential problems with it have a look here
http://www.hennapage.com/henna/ppd/ppdmed.html and here
http://www.hennaforhair.com/ppd/index.html Both pages link forward to further, peer reviewed medical information about it.