Petrolatum/Petroleum contains Mineral oil that actually accumulates on the scalp and this blocks the hair follicles, slowing hair growth. If it builds up on the hair itself, it attracts and holds dirt and residue, which make the hair appear dull and unhealthy. You can see this build up when you wash your hair the amount of dirt that is accumulated can often be seen washing out.
Petroleum is a natural extract from Crude Oil yes the oil used in cars etc and for this reason it does not have a lot of vitamin or necessary components that your hair needs .Mineral oil found in Petroleum does not penetrate the hair shaft it only coats the hair and serves as a temporary “solution” for making the hair look slick and shiny.
Due to it’s insoluble nature, petrolatum is able to block in moisture(water) within the skin/scalp. Petroleum aka petrolatum is actually a highly effective sealant. If your hair is properly moisturised using a petrolatum-based product on top will completely stop any moisture coming in or going out. But that’s where the benefit stops, the same benefit is also a disadvantage because petrolatums and mineral oils leave a heavy film over hair making any following moisturising efforts hard or even completely pointless.
Petrolatums and mineral oils have no moisturising ability at all. If your hair is looking sleek and shiny after you use them, it’s nothing to do with moisture, these chemicals just happen to be greasy-textured so that glow is purely cosmetic.