Greetings~
Botox doesn't have to cause a shine when injected into the forehead. There are a combination of factors comin in to play that create this shiny, glass-like appearance. Botox has an effect on not only the muscles of the forehead, which when overly relaxed by perhaps too much botox can cause not only a lack of any movement but also a smooth, shiny, almost glass-like appearance. A definite no-no for anyone that wants to combat wrinkles but still look natural. Botox can also effect the oil and sweat producing glands in the skin which can also change the overall appearance of the skin. One more reason that less is best for a great result. (more can always be added if need be)
Best~
Dr. Grant Stevens