Have light blotches all over my back, what may cause that?

T. versicolor?: Only an examination by a physician can give you a definitive answer. One possible cause of painless non-itching non-elevated less-pigmented areas is a superficial fungal infection called tinea versicolor.

Rash: would need a picture an more information ---to determine if the rash is allergic or infectious--a common rash that can fit your description is Pithyriasis Rosea--this is a common dry patchy rash----that frequently is itchy---and can persist for 6-8 weeks----look this rash up on he internet and see if it fits your rash---follow up with your private doctor soon

Light blotches: Light blotches can occur on a persons back if they have been exposed to sun. There is a condition called tinea versa color that causes light splotches on the back as well as arms. You should see a dermatologist.