Ok, so after reading about all the controversy surrounding MTG, I decided to email the president of Shapley's myself and inquire about any dangers of human use of this product. I use it and have not had any problems.
Here is her reply:
Thank you for your email regarding use of Original M-T-G on human hair.
As you mentioned, it was originally formulated for use on human skin ailments. As I was not the owner at the time (it was in the 1930's) I can only guess at why they did not pursue the human market. From the history that I have for the company, when Henry Shapley, who was a barber, realized it worked well on horses, also, he started a side company selling it. This is the company that he sold and eventually became my current company. My guess is he still used the formula on his own clients and then when he retired, it fell by the wayside. Now, as I have not been able to speak directly with Henry, or his family, this is supposition that I have gained from the previous owner.
With all that being said, I can tell you that none of the ingredients in the current formula for Original M-T-G have any known detrimental effects on humans (with the exception of an allergic reaction to sulfur). We have had the formula reviewed by a human hair care specialist (PhD with FDA experience) and he has given us the ok to pursue the human market with the current formula.
This is what we are doing currently. We are tweaking the formula to improve the smell and the consistency, but these are only cosmetic changes. We hope to have this available to market soon.
I hope this helps to alleviate your concerns about using the product. If not, please do not hesitate to contact me.
Best regards,
Cindy S. Carfore
President, Shapley, Ltd.
HTH!!!