vaseline petroleum jelly is a mixture of mineral oils, paraffin and microcrystalline waxes that, when blended together give a smooth jelly that has a melting point just above body temperature. it literally melts into skin, flowing into the spaces between cells and the gaps. vasline helps in keeping the outside world out - it protects skin from the effects of weather and exposure. Second, it acts like a sealant to help keep the inside world in - it forms an occlusive barrier to the natural water loss of the skin. So skin that is dry and chapped is protected from drying elements, enabling skin-softening moisture to build up naturally from within the skin.