Q.1:- Assume that I have applied some oil or gel or wax to my hair and I am doing wuzu. My question is that when I do masa on such hair, does wuzu become invalid? why.

Q.2:- Assume that I have applies some kind of oil on my face and it is transparent and so I start to do wuzu. So when I wipe my face with water on the skin of face, my wuzu becomes invalid? why.

thanks alot

Because it stops water according to ruling water should reach.