What is the difference in the percentage of minoxidil ?

Topical minoxidil usually comes in 5% strength.  Higher percentages would mean there is more minoxidil concentration.  Higher percentages do not mean it will work better.

It's a common question. Minoxidil is only FDA approved for 2% and 5 %. Not 10%, not 15 %. Not 17.5%. I have seen many, many patients with dizziness, headaches, heart palpitations at the higher doses- and a few who feel extremely unwell. Any use if minoxidil above 5% is an off label use and carries unknown risks. Furthermore, there is absolutely no scientific proof that higher concentrations are consistently better than the FDA approved strengths. 

The percentage is just the concentration of minoxidil. 2% and 5% are the only two FDA approved. The higher the concentration above 5% does not mean you will get that much better results.