Is phillip's milk of magnesia (magnesium hydroxide) harmful if you put it on your face everyday to control oil?

Depends: Milk of magnesia (magnesium hydroxide) is full of some good things for skin, like magnesium, and zinc, and it has anti-bacterial properties. It has been mentioned as a way to control acne when it is used as a mask. It works best for oily skin. However, it is very drying, and so can cause problems for people when used too frequently, or if left on too long, or if your skin becomes dryer, or if you are allergic to it.