Question:
Does applying oil that moisturizes the skin affect the validity of fasting, especially if it is of a type that does not prevent water from reaching the skin?
Answer:
There is no harm in applying oil while fasting, when needed. This is because oil only affects the outer layer of the skin and does not penetrate into the body in a manner that would invalidate the fast.
Even if it were assumed that some oil components are absorbed by the skin, it still does not break the fast according to Islamic rulings.
Shaykh Ibn Jibreen (رحمه الله)