Pepper spray in Michigan is legal with some restrictions.
Human spray must contain 10% or less OC, and can only be used for self defense. The following is quoted from the Michigan Penal Code; "The reasonable use of a self-defense spray or foam device containing not more than 10% oleoresin capsicum no more than 35 grams (1 oz=28.35 grams) by a person in the protection of a person or property under circumstances that would justify the person's use of physical force."
To sum it up... 10% or less OC human sprays only. You may purchase any animal repellents such as dog or bear sprays regardless of their OC count since they are used against animals and not humans.
The products listed below are legal to buy for Michigan residents: