The hair that you see, is dead, so putting something on it can only affect the dead hair. Its like your nails.
I cannot imagine how putting anything on the scalp will affect blood flow, but I guess a lot of people make money out of selling products with exaggerated claims, many of which do not work.
If you are really worried see your GP and if he/she thinks there may be a problem he/she will probably refer you top a dermatologist. (Hair expert)
(Incidentally, if a person has been poisoned over a period of 6 to 12 months, with arsenic, the poison levels can be detected in the hair and the nails. It's possible to be fairly accurate in determining how was was taken and when)
